Rheinmetall to develop 130 mm gun and upgraded 120 mm gun

A presentation from Rheinmetall's Capital Markets Day 2015, an outlook for the investors held in November last year, includes a few very interesting informations about the future of Rheinmetall Defence. Rheinmetall is developing an upgraded 120 mm high-pressure gun and a new 130 mm gun.

For the future of the Leopard 2 main battle tank (MBT), Rheinmetall is seeing a three step program:

1. Modernization of the Leopard 2 with new technologies including an high-pressure 120 mm gun
2.  Upgunning the Leopard 2 with the new 130 mm gun being developed by Rheinmetall
3.  Replacing the Leopard 2 with the Main Ground Combat Systems

The modernization of the Leopard 2 suggested by Rheinmetall is pretty much identical with the MBT Technologieträger and it's new technologies. An interesting standout feature here is however the "new 120 high-pressure cannon and ammunition", which will offer a 20% increase in performance. This leaves a lot of room for speculations: One possibility could be that the "new" gun is refering to the already existing 120 mm L55 gun and this statement is related to the 103 Leopard 2A4 tanks, which were bough back from the German industry by the German Army in 2015. These tanks will be upgraded in the near future to work together with the 225 Leopard 2 MBTs currently in service, which are all in the 2A6, 2A6M or 2A7 configuration. It is known from data provided by Rheinmetall, that the L55 gun provides 15% higher muzzle energy than the shorter L44 when firing the DM53 ammunition; the 20% could be the result of a new type of main gun ammunition (then designated DM73), which has been confirmed to be in development in 2015.
Another possibility is an increase in barrel length, mentioned by Autobild.de, the first source to mention the 130 mm gun. Autobild.de is not a military related source, but they were invited to a presentation of the MBT Technologieträger prototype. According to them, an increase of 1 meter in barrel length is a possibility (but my original interpretation of their words was that they talked about switiching the Leopard 2 Revolution prototype from L44 to L55 gun). If this makes sense, given the drawbacks affiliated with a longer gun barrel, is questionable in my opinion.
A third option would be upgrading the L55 gun, but only by using more modern components instead of lengthening the barrel. As the barrel has to be replaced on a regular base (due to barrel wear), a cheap option would be the replacement of the gun barrel with a more modern one, which due to better manufacturing processes (such as a higher pressure for autofrettaging) and/or better metallugry can deal with higher pressure ammunition. This has been done in the past at least by the US and probably also by some Leopard 2 users.

Rheinmetall announced to develop a new/upgraded 120 mm and a new 130 mm gun

The development of the 130 mm gun is quite a surprise. When originally mentioned by Autobild.de, I assumed they had made a typo and refered to the original 140 mm NPzK tank gun being developed in the late-1980s and 1990s. Given Rheinmetall's plans to upgun the Leopard 2 with the 130 mm gun and the smaller calibre, it seems reasonable to assume that the new gun is physically smaller than the 140 mm NPzK tank gun, which proved to be too large for the original Leopard 2 turret (also due to requiring an autoloader). However it seems that the new gun will provide similar or even better performance than the canceled 140 mm gun: Given that a current DM53 APFSDS has an energy output of nearly 13 MJ according to Rheinmetall (or 0.2 - 0.3 MJ less according to calculations based on muzzle velocity and weight), the 130 mm gun (which according to the presentation provides 1.5 times as much performance), should provide a muzzle energy about 19.5 MJ at least - if the 1.5 times more performance is meant in relation to the "new 120 high-pressure cannon and ammunition", which already provides 20% more power than the current 120 mm gun/ammo - then a muzzle energy of 23.4 MJ could be reached! Just for reference, the 140 mm gun supposedly had a muzzle energy of about 20 MJ. How exactly the new gun will achieve such a big performance leap is unkown; making the ammunition larger without opting for an autoloader or two-piece ammunition is not possible. Using two-piece ammunition could enable the Leopard 2 to retain it's crew of four, as done on the Swiss prototype with RUAG 140 mm gun, which was manually loaded.
Rheinmetall has at least confirmed that the new gun will be marketed beginning in 2016, so we might see a few further posts about this topic in this year.

A possibility for both tank guns mentioned by Rheinmetall is also the use of new technologies, such as an ETC gun. Already in the year 2000 an ETC gun prototype managed to outperform a L55 tank gun using a projectile of the same weight. This was published in the European Forum on Ballistics of Projectiles, article "Status and Results of the German R&D Program on ETC Technologies". The LKE II (DM53 prototype) fired from the L55 gun reached a muzzle velocity of 1750 meters per second (mps) at 21° centigrade, whereas a projectile with the same mass, fired from the ETC prototype gun with 110 KJ of electrical energy added, managed to reach a muzzle velocity of 1822 mps and an energy output of 14 MJ.

Please note that this rendering shows a Leopard 2 Revolution

The new 130 mm gun is a precondition for the Main Ground Combat System (MGCS). The Main Ground Combat System is currently being developed by Germany and France as replacement for the Leopard 2 and Leclerc main battle tanks, although Rheinmetall is expected other nations to join into the MGCS development.
The contract between Germany and France for the development of the MGCS was signed originally in 2012, despite becoming only wider known after the new Russian T-14 Armata MBT was revealed in May of 2015. It is understood that the MGCS is currently in the conception phase; different concepts are being made and evaluated, while new technology is being researched and tested. The conception phase is expected to last at least until 2017.

Informations on LAND 400 Phase 3 candidates

The Australian Defence Technology Review has published an interesting article on the third phase of the LAND 400 program of the Australian Army. The LAND 400 program is the planned replacement of the currently outdated equipment of the Australian forces - such as the ASLAV and the M113 - with modern state-of-the-art vehicles.

Part of the phase 3 is the procurement of a planned 450 medium-weight tracked vehicles, of which 312 will be fitted with a turret in an infantry fighting vehicle (IFV) configuration.
As of today, three contenders for this contract are known: The German company PSM (a joint venture of Rheinmetall and KMW) will offer their Puma IFV, BAE Systems is reportedly offering the CV9035 and General Dynamics is supposedly offering a vehicle based on the ASCOD 2.
The Puma is one of the latest IFVs, with the first Puma entering service in June 2015. It's probably the heaviest armored IFV available on the market and is fitted with a number of advanced features like a decoupled running gear with hydropneumatic suspension, third generation thermals, a softkill active protection system (APS) and a modern fire control system (FCS) with independent commander's sight. The Puma will be armed with a 30 mm MK-30/2 ABM autocannon with athe ability to fire airburst ammunition, a coaxial machine gun, a dual-purpose Spike-LR ATGM launcher and an independent grenade launcher mounted on an elevatable mast. The Puma has not been fitted with an remote weapon station (RWS) yet.
It is powered by a 10 cylinders MTU MT892 engine which is fitted in combination with a version of the HSWL 256 transmission from Renk. It provides an output of 800 kW.

The Puma IFV is the newest vehicle competing for LAND 400

It seems to be rather clear that the Puma should be able to fullfill all armor and protection requirements, given it's weight, the German requirements and the extensive amounts of armor.
Problems for the Puma are at least the lack of a turretless version for the non-IFV version, the rather huge price tag and the lower troop carrying capacity.

The ASCOD 2 is based on the development of the Ulan (pictured) and Pizarro IFV

Which version of the ASCOD 2 might be offered to Australia is unkown yet. The latest vehicle based on the ASCOD 2 is the British Army's Ajax, which will utilize the CTAS (case telescoped armament system) 40 mm gun (but the Ajax is not an IFV and transports no dismounts). The CTAS gun offers more punch than the 30 and 35 mm autocannons of the  Puma and CV90, but suffers from lacking commonality with the planned 8x8 vehicle (for this GD offers the LAV 6.0 with 30 mm Kongsberg unmanned turret). Thus the ASCOD 2 version for the Australia is expected to be offered with a 30 mm Bushmaster II gun mounted in either a manned or unmanned turret. The early ASCOD 2 prototypes utilized the same SP-30 turret as the Ulan of Austria and the Pizarro of Spain, the original ASCOD 1 versions. This turret is manned by a crew of two and mounts a MK-30/2 autocannon from Rheinmetall, the previous version of the Puma's gun. While the Ulan and the Pizarro have been fitted with different fire control system, it seems that none of this is hunter-killer capable, despite both providing separated sights for the gunner and commander. These two FCS (made by Kollsman/Elbit and Indra respectively) are the only known to be fitted to the SP-30 turret. The ASCOD 2 utilizes the MTU V8 199T21 engine, which provides an output of 600 kW (about 800 hp). The engine is used in combination with the HSWL 256B transmission from German company Renk.

An ASCOD 2 APC presented on Eurosatory 2014

However the original ASCOD design is lackluster at a few other places. Except for the current Scout-SV vehicles, such as the Ajax revealed last year at DSEI 2015, the ASCOD lacks a high performance anti-mine kit and heavy armor solutions. The basic ASCOD 2 is protected against 14.5 mm AP ammunition in accordance with STANAG 4569 level 4, although even the old flyers from several years ago mention the possibility of up-armoring the ASCOD 2 to level 5 (protection against 25 mm ammunition allong the frontal arc). No version of the ASCOD 2 has been presented with an RWS ontop of the turret, but a special APC version with RWS has been produced. The ASCOD 2 might also have issues with the 8-men squad requirement from the Australian Army - while the Ulan can carry 8 soldiers, the Pizarro (due to different interior arrangement and troop equipment) transports only a 7-men squad. The ASCOD 2 utilizes most likely decoupled mine-safe seats (like the Puma) and proper decoupled equipment storage, which makes it rather improbable that without deeper modifications an 8-men squad can be transported. Unlike the Puma, the ASCOD 2 will probably not offer an integrated ATGM without extra costs.

A CV9035 of the Koninklijke Landmacht

The Combat Vehicle 90 Mark III (CV9035) is the most proven of the three vehicles, being in service in the Netherlands, Denmark and was recently ordered by Estonia. The CV9035 uses the E35 turret armed with a 35 mm Bushmaster III gun from ATK. The same turret is also offered for the Patria AMV35 and thus the CV9035 would offer a great benefit in terms of commonization of parts and spares, if the AMV35 is chosen over it's competitors.
The CV 90 Mk. III is powered by a Scania V8 engine with an output of 600 kW. The basic vehicle is constructed from steel, providing protection against 14.5 mm AP and 23 mm API along the frontal arc. However like the ASCOD 2, the CV9035 is pretty much always fitted with applique armor to boost the protection level to STANAG 4569 level 4 and/or level 5 at least. Further armor kits and mine-protection kits for the CV9030 and CV9040 have been developed, it seems reasonable to assume that those armor kits can be modified to CV9035 compatability. While BAE's brochures claim that the CV90 has hunter-killer capability, it seems that this is dependent on the exact FCS version fitted, which differs depending on user's configuration.

The Armadillo APC is a turretless CV90

A turretless version of the CV90 is already existing with the Armadillo APC. Unlike the ASCOD 2 and the Puma, there is at least a version of the CV9030 fitted with an RWS ontop of the turret; the possibility of adopting the same to the CV9035 seems to be given. 
The CV9035 however is also the oldest designs and suffers from more drawbacks. Like the ASCOD 2, the CV9035 lacks an ATGM armament for fighting heavier armored targets and/or helicopters. While the 35 x 228 mm caliber of the Bushmaster III gun packs about 50% more punch than a 30 x 173 mm round of the MK-30, it's much larger physical size has a very negative impact on ammunition stowage. While the Puma and ASCOD 2 (with SP-30 turret) both can carry 200 rounds loaden at the gun, the CV9035 has only 70 rounds available at the gun. The total ammunition stowage is also much lower. Furthermore the CV9035 is also not able to meet the 8-men dismount squad requirement of the Australian Army in it's current configuration deployed by the Dutch and Danish armies.
Lastly the ballistic and mine protection of the CV9035 seems to be relatively low compared to that of the Puma and ASCOD 2. While armor packages are available, these might need additional reconfiguration to the exact CV9035 layout and

It is interesting what currently seems to be happening in the SEA region. Australia is planning to acquire huge numbers of state-of-the-art wheeled and tracked vehicles, while many NATO countries including the US have to cut back most of their military procurment plans due to funding issues. There are a number of issues and unkown factors with the Austrlian LAND 400 program still: We don't know if other contenders will or already have responded to the tender for the tracked vehicle aswell. Currently we only know that the Puma - apparently most likely in the standard German Army configuration - the ASCOD 2 in an unkown configuration and the CV9035 in a somewhat unkown configuration will compete for the contract. All three of the previous mentioned vehicles might have trouble with the Australian Army's requirement for transporting a 8 men squad of dismounts and have other individual issues each. From my point of view the Puma might be the best bet, but also the most expensive. In terms of protection, technology and the armament concept (once the integration of the Spike-LR and the grenade launcher are finished) seems to be the most promising. The lack of ATGM armament on the other vehicles would be a no-go for me, but we don't know what GD and BAE will change for Australia. But who knows what the Aussies want, in the end they happen to have one of the most scatterbrained and odd mechanized infantry concept out there.
The LAND 400 phase 2 will probably already be a preliminary decision, it seems likely that the winner of one contract will have a huge benefit in the other due to the ability of keeping parts exchangeable and cutting costs down.

M829A3 APFSDS penetration power - common internet estimation failures?

The M829A3 is currently the latest type of APFSDS ammo in service with the United States armed forces. It replaced the M829A2 in 2003.
In the next year(s) the M829A4 will take over the place of the M829A3. It is already confirmed to have the same exterior dimension and general characterisitics as the M829A3, but utilize an improved penetrator designed to penetrate even newer types of ERA ("3rd Generation Explosive Reactive Armor").

The M829A3 APFSDS of the US Army

In order to estimate the penetration power of APFSDS different mathematical fomulas can be used, such as the formula developed by Lanz and Odermatt for the Swiss military procurment agency. This formula has gained most acception in also mentioned in different documents of the US Army Research Laboratoy. It is an empiric forumla, which means it's a mathmatical interpolation of actual tests results in dependence of the changed parameters (density, length, diameter, etc.).

The M829E4 is confirmed to have the same dimensions as the M829A3

On different forums such as Tank-Net, the WoT forums and for different software, such as the Steelbeasts simulator/game from eSim Games, people have tried to calculate/estimate the penetration power of the M829A3 APFSDS based on measurements on photographs and available data from the manufacturer's website.
However most of these people are assuming a penetrator length of 780 mm to sometimes even above 800 mm! This is solely based on the increased length of the in-flight projecitle and the assumption that the M829A3 uses a "stepped" tip assembly like the M829A2 APFSDS. This way, the estimated penetration of the M829A3 APFSDS from the 44-calibre long M256 gun against rolled homogenous steel (RHS) reaches or even exceeds the penetration of other types of ammunition fired from the longer Rheinmetall L/55 gun. Penetration values above 750 mm into RHS after 2 kilometres are commonly estimated for the M829A3.

Does the M829A3 possibly look like this?

However patents from Alliant Techsystems (ATK) show us a different possibility of the M829A3 design: instead of utilizing an elongated DU penetrator with conventional tip to defeat tanks fitted with heavy ERA by "brute force", it is suggested to use a special tip assembly to overcome ERA. The tip is a solid steel construction with a length "greater than 100 mm", while the main penetrator has a length of "about 630 mm, preferably greater than about 650 mm, and more preferably greater than about 670 mm". Specifically the last value is interesting, because this is very close to the reported length of the penetrators used in the previous M829A1 and M829A2 APFSDS rounds. Furthermore the thickness of the rod was increased from 22 to 25 mm, which result in a 67% higher bending stiffness (and thus better performance against ERA).
Such a penetrator design has a big benefit against targets protected by heavy ERA, which is what the main target of the M829A3 development was. The solid steel tip will punch a hole into the ERA, but is designed with a special weakpoint at the connection to the main penetrator; it will break of instead of transfering the stress created by the interaction with the ERA-plates onto the main penetrator. While the M829A1 was unable to defeat the contemporary Soviet tanks with Kontakt-5 heavy ERA, the M829A2 was designed as "brute force" solution against Kontakt-5 armed Soviet tanks. The M829A3 was the "elegant way" to defeat better armored tanks with Kontakt-5 or the follow-up ERA.

There are further reasons to assume that the M829A3 APFSDS follows the above mentioned design:
Unlike it's three direct predecessors, no M829A3 cut-through model has ever been displayed, while cut-through models of the earlier APFSDS types were presented while they were the latest stuff the US Army had. 
Furthermore there is the weight growth of the M829A3 compared to the M829A2. While the sabot material was changed - an improved compostion reduced the density - the overall sabot weight of the M829A3 is understood to be higher to due the much longer sabot petals. Values from the US laboratories responsible for developing/manufacturing (composite) sabots for the M829 series show that the sabot weight of the M829A3 should be 3 kilograms and that of the M829A2 should be about 2.4 kg. A 780 milimetre long DU rod with 25 mm diameter will already weigh 7.08 kg and thus be a contradiction to the 10.0 kg weight for the complete projectile assembly from ATK's brochures. A rod with a length of about 680 mm and a 25 mm diameter made from DU  however will weigh about 6.18 kg and thus leave about 0.6 kg for tracer, fin assembly and the 100 mm steel tip. Given that a 100 mm steel rod with 25 mm diameter weighs about 400 grams, assuming that the M829A3 uses a 680 mm DU rod with 100 mm steel tip seems to be very reasonable based on the weight.

The US Army had no problems showcasing a cut-through M829A2

What impact does this have on the penetration estimates mentioned earlier? According to the patents from ATK, such a design increases the penetration into RHS protected by an unkown type of heavy ERA by 20 to 30% compared to the same penetrator without solid steel tip. Against normal RHS not protected by any form of ERA however the penetration increased only by 5 to 10%, which is to be expected due to the steel tip also prodividing penetration.
The M829A3 might as well be optimized for fighting tanks with heavy ERA such as the main tanks of all potential enemies of the US/NATO - China, Russia, North Korea all utilize heavy ERA on their latest tanks. So instead of having some mind-boggling penetration (for an APFSDS fired with the short L/44 barrel) against all types of armor, the penetration against RHS/composite armor might be as low as ~660 to 700 mm; enough to defeat the main armor of tanks like the T-80U, T-90 and Type 99.

Penetration of APFSDS with steel tip vs conventional tip

Germany and the Netherlands increase military cooperation

On the 4th of February, Germany and the Netherlands announced a closer cooperation of their militaries. This process was already reported earlier in late 2015.

German and Dutch Defence Ministers signing a letter of intent

About 3000 Dutch soldiers from the 43rd Mechanized Brigade of the Royal Netherlands Army will be integrated into the 1st German tank division, together with the last 16 Leopard 2 tanks from Dutch stocks. 2 further Leopard 2 tanks will be rented/bought by the Netherlands to get to the 18 tanks required for a tank company. All of these tanks are understood to be upgraded in near future to the latest Leopard 2A7 configuration.

The Leopard 2A7 tank entered service in late 2014

On the other side a 400 men strong mixed brigade will be put under Dutch command. This will include a German tank battalion to be stationed at Loheide/Bergen in Lower Saxony, Germany.

The closer cooperation of the German and Dutch land forces already started in 2014, when the 11 Luchtmobiele Brigade (11th air-mobile brigade) was integrated into the structure of the German Division Schnelle Kräfte.

Regarding naval forces, both the German and Dutch government have agreed upon a letter of intent, which includes plans of the German Navy being allowed to utilize the Dutch Karel Doorman support ship, while the German naval battalion will be integrated into the structure of the Dutch marine corps, but not be relocated to the Netherlands.

The Karel Doorman support ship

 Such European cooperation can be beneficial for all partner: Germany will probably not buy new support ships, despite originally planning to order two new ones; the Dutch Navy on the other hand had troubles affording the Karel Doorman, so German money will help out a lot.
Without the integration of the Dutch tanks into the German Army, the Netherlands would lack two tanks for having a whole company and the support structure related to using MBTs after retiring all Leopard 2 tanks a few years ago. On the other hand Germany has only enough tanks and soldiers to create the new 414th tank battalion thanks to the Dutch tanks.

CR2 upgrade contenders

According to Jane's IHS, several contenders are in the run for the Challenger 2 LEP upgrade contract.

The contenders that send bids to the UK Defence Equipment and Support (DE&S) are:

• BAE Systems Combat Vehicles
• General Dynamics Land Systems UK
• Lockheed Martin UK
• Krauss-Maffei Wegmann
• Rheinmetall
• CMI Defence
• RUAG Defence

The Challenger 2 life extension programme (LEP) was announced some time after the reveal of the T-14 Armata tank in Russia during the Moscow Victory Day Parade 2015. At first the UK MoD also considered buying a completely new main battle tank (MBT) as replacement of the Challenger 2. In particular the lethality and the effectivity of the L30A1 tank gun has been questioned.
Unlike other tanks such as the M1 Abrams and the Leopard 2 MBTs, the Challenger 2 has not seen any major upgrades since it's introduction into British Army service in the 1990s. The British Army already investigated the replacement of the rifled L30 gun with a German Rh 120 L/55 smoothbore gun during the Challenger 2 lethality improvment programme (CLIP) beginning in 2001, but this project was terminated due to too high costs. The German gun together with the superior tungsten ammunition proved to be more effective during the British trials.
The follow-up to CLIP was the Challenger 2 capability sustainment programme (C2 CSP), which incorporated most parts of the CLIP and some new upgrade ideas. However the C2 CSP also ended up being too expensive and was thus terminated in 2008.
The Challenger 2 LEP was announced in July 2013 and started one year later. The reveal of the T-14 Armata however triggered however the UK's interest in owning a tank strong enough to cope with the T-14.

The Challenger 2E is the most advanced version of the CR2 to be developed by Vickers/BAE yet.

The list of contenders is rather interesting. BAE as owner of Vickers has the in-house advantage, but has not gathered any experience in modern tank design/building since the Challenger 2. Even worse BAE had to rely on the purchased Hägglunds for any sort of the success on the AFV export market in the recent history. In theory BAE might fall back to the old Vickers Challenger 2E tank designed for export, which failed to perform equally well as the Leopard 2, Leclerc and M1 Abrams in the Greek trials in the early-2000s. The Challenger 2E offers a number of considerable upgrades over the current CR2: a EuroPowerPack (MTU MT883 engine together with Renk HSWL 295TM transmission) and a new, superior fire control system with the SAGEM MVS 580 periscope and SAGEM SAVAN 15 gunner's sight. However BAE announced in 2005 that the development of the CR2E was stopped following lack of success on the export market.

General Dynamics is having the Abrams as up-to-date modernized MBT. While the upgrades might not be as deep as the ones offered by other companies on the market, this seems to be largely related to the lack of funding from the US and the low interest in upgrading foreign M1 Abrams tanks (due to the fact that most Abrams user's like Egypt, Iraq and Australia do not have the money for any tank upgrades).
For the Scout-SV programme General Dynamics European Land Systems however had to rely quite a bit on other companies from this list: the turret for the Ajax is based on Rheinmetall's Lance Modular Turret System and at least partly manufactured in Germany, whereas Lockheed Martin UK has developed the fire control and reconnaissance systems for the Ajax.

The upgraded Warrior using Rheinmetall's turret design as base is the best reference that LM can offer.

Lockheed Martin plays a major in the Warrior capability sustainment programme (WCSP) and in the Ajax variant of the Scout-SV, but lacks any own vehicle designs. Instead LM mostly upgrades electronics and other sub-components of AFVs mostly. For the Scout-SV and the WCSP Lockheed Martin relied on turret technology supplied by Rheinmetall and technology/components supplied by other sub-contractors.

Krauss-Maffei Wegmann (KMW) is currently the world market leader when it comes to tanks and thus should be considered a very safe bet. While on pure numbers the M1 Abrams and the T-90 have sold more units, this is often the case by allowing the local assembly of cheap, downgraded and subsidized versions (such as the M1A1 tanks for Egypt or Iraq and the T-90S tanks for India). KMW has shown the willingness to create local versions of the Leopard 2 and to allow local assembly. They also have shown intention to upgrade designs made by other companies (such as their bid to upgrade the Brazilian M113s). During the 1980s and early 1990s KMW developed a special tank based on the Leopard 2 tank for the Spanish Army. KMW could just as well "leopardize" the Challenger 2 by fitting the Challenger 2 with as many proven sub-system of  the Leopard 2 as possible.

Rheinmetall has seen increased success on the tank market, after starting to compete against KMW for Leopard 2 upgrades in 2010. They just recently managed to win a contract for the modernization of the Polish Leopard 2A4 tanks to a new Leopard 2PL standard. Rheinmetall has a wider variety of subsidaries and can probably, unlike pretty much any other contender, provide most technologies and components by themselves, without the need to hire a subcontractor.
With the MBT Revolution upgrade, Rheinmetall does already offer a modular upgrade which in theory is designed to fit (with some adaption) to any tank. So maybe we can see some type of Challenger 2 Revolution?

Leopard 2 Revolution prototype - will the CR2 soon look similar to this?

CMI Defence is probably the least expected candidate for the Challenger 2 LEP tender. It never has produced or designed a complete AFV or even a major AFV upgrade. Instead CMI Defence is specialized on light-weight medium/large caliber guns (such as the series of Cockerill 90 mm guns or the Cockerill CV 105 gun) and making ammunition for these. However in the past years CMI has extended it's portfolio into the market of turrets and weapon stations.

CMI's biggest turret on a CV90

RUAG Defence of Switzerland has experience with the modernization of medium and heavy combat vehicles for the Swiss Army and several other export costumers. The Panzer 87WE upgrade for the Swiss Army was developed in cooperation with KMW, previously RUAG also upgraded the Swiss fleet of M109 howitzer. Other tank modernizations from RUAG include upgrades for the older Panzer 68 and cooperation with Jordan on the M60 Phoenix MBT prototype. In 2015 RUAG has managed to win a contract for upgrading Austrian and Belgian Pandur APCs.

Currently RUAG is offering a Leopard 2A4 upgrade - does it work for CR2 aswell?

In general it is unkown how the UK MoD wants the CR2 to be upgraded. It is understood that the scope of the upgrade is rather limited, as the budget is very tight. Replacing the gun is expensive, because the interior of the Challenger 2 MBT is not configured for storing long 120 mm unitary rounds. In case of the CR2 fitted with the German L/55 gun as prototype during the CLIP, there was only proper stowage space for a total of 6 rounds (!) of main gun ammunition.

This 6 round compartment stores all the ammunition of the CLIP prototype...

In theory only Rheinmetall and RUAG/CMI can offer a main gun replacement with their own technology. Rheinmetall has developed the Rh 120 L/44 and L/55 guns of the Leopard 2 MBT, aswell as a 105 mm smoothbore gun and the 120 mm L/47 LLR (lightweight, low-recoil) gun.
RUAG has developed the 120 mm CTG (compact tank gun), which was designed with reduced recoil as a low-cost/low-modifcation upgrade option for various existing tanks. Jordan has tested this gun on a Challenger 1 tank, the M60 Phoenix upgrade prototype and on the Falcon-2 turret system, BAE used this gun for the CV-90/120 light tank and the Swiss Army trialed it on their Panzer 68 upgrade.
Depending on required maximum recoil and muzzle break, the CTG has a length of 47 to 51 calibres.

Will CMI or RUAG offer the CTG to the UK?

However it is unclear wether RUAG or CMI could offer this gun to the British Army (even if they could afford major modifcations to the CR2 interior) - CMI has bought at least some rights of marketing the CTG to at least some markets. Maybe CMI bought the full rights, or RUAG and CMI agreed on both having full rights for this design. 

Another interesting concept, that however might as well be too expensive for the British Army, just as fitting a smoothbore, is the idea of mounting a new turret on a Challenger 2 hull. The turrets of the M1 Abrams and of the Leopard 2 can fit onto the turret ring of a Challemger 2 hull, but require some deeper modifications, which again could be too expensive for the British military. The M1 Abrams turret does not include most of the gun and turret drives, which are located in the tank's hull and are also hydraulic in the M1 Abrams. This is an important difference to the CR2 turret, which includes electric gun and turret drives. US trials have also revealed that upgunning the M1 Abrams with the longer L/55 gun of the Leopard 2A6 requires deeper modifications, which is why it was judged as being to expensive for the US Army. The big advantage of a M1 Abrams turret would be the rather large ammunition load of 34 or 36 rounds (depending on which racks are installed).
The Leopard 2 turret has electrical drives housed in the turret, so that it would be easier to integrate onto a CR2 hull - however the Leopard 2 stores only 15 round main gun ammunition in the turret buslte, so that the CR2 hull would require modifications for storing further ammo.
CMI is specialized on guns and turrets, so they could offer a version of their Cockerill XC-8 105-120HP turret fitted with a 120 mm smoothbore gun, if the turret rings are compatible. Problematic is in this case the different level of protection (CMI's turret is lacking thick composite armor) and the fact that the British Army might not like being forced to utilize an autoloader.

According to Jane's IHS only two contenders will be shortlisted. I'd bet that this will be BAE and either General Dynamics or Lockheed Martin - simply because they have the best position in British politics and they have manufacturing facilities in the UK. The UK government was willing to increase the price tag for their Scout-SV programme by several millions, just to move the manufacturing site from Spain to Wales.
In terms of technology, I'd choose Rheinmetall, General Dynamics or KMW however. Unlike BAE these companies have state-of-the-art products available and do not make most of their living from old 1980s designs such as the Warrior or Bradley. Compared to CMI and Lockheed Martin, all of these companies do have manufacturing capabilities for deeper modifications and upgrades. RUAG is probably comparable, but lacks a wider portfolio and as many successfull contracts as Rheinmetall/KMW/GD.

Probably the Challenger 2 LEP will end up being only a minor improvment due to budget cuts. Some new ammunition maybe, an improved fire control system, a new APU and maybe some other digital stuff.

Why rating tank armor and penetration into RHAe is wrong

People on the internet and even some authors of military textbooks and magazines often pretend that armor and penetration can be accurately measured in milimetres of equivalent steel thickness. They use a so-called rolled homogenous armor equivalency (RHAe) to rate the performance of special armor in comparison to rolled steel (RHA o RHS). 
The logic is simple: When a projectile penetrates X armount of steel armor, but only X-Y after penetrating a certain type of special armor, then Y is the protection provided by this armor. To a certain degree RHAe has been used in science, but to a much more limited extend than people on the internet and many authors of books focused on tanks pretend.

There are many different examples which however show that this is not the case. Relatively simple spaced armor used to provide considerable protection against earlier types of AP(FSDS) ammunition, but has been rendered useless by more modern APFSDS designs. Kontakt-5 used to be highly effective against APFSDS, but modern APFSDS design and improved metalugry make it obsolete. ERA and NERA are highly effective against shaped charge warheads, but warheads with precursor charges and tandem charges perform very well against most types of (N)ERA.
But also the exact shape and design of the used ammunition will affect the efficiency of modern special armor. The Soviets experimented with DU as material for HEAT ammunition and even adopted one type of DU-HEAT, despite this ammunition not performing better against RHS; against special armor however the DU-HEAT was considerable better.

This also affects the supposedly superior penetration of DU compared to tungsten penetrators. According to US studies, penetrators made from tungsten-iron-nickel (W-Fe-Ni) alloys had between 8 and 10%¹ less penetration depth into rolled homogenous steel targets than DU penetrators.

An example about how big the difference between penetration into special armor and RHS is given in a scientific study of different penetrator designs.² The penetration of conventional monoblock penetrators and jacketed penetrators into a block of steel and a block of steel protected by spaced armor is compared.
Both penetrators have an aspect ratio of 25 to 1 and are fired with the same propellant. The jacketed penetrator is a tad faster, due to the steel jacket fitted to the tungsten penetrator weighing less than the tungsten of the unitary penetrator.
Against normal RHS, the jacketed penetrator had a 12% lower penetration compared to the unitary one - against the target protected by spaced armor however, it had a 17% higher penetration depth! So while any "RHAe values" would put the penetration of an unitary penetrator above that of a jacketed one, the reality shows that against more complex armor systems the jacketed penetrator might be a lot better.

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1 - The values for the lower penetration of tungsten vs DU into semi-infinite RHS targets comes from "Tungsten Alloy Properties Relevant to Kinetic Energy Penetrator Performance" from Downing et al; but improved tungsten alloys have mimicked DU's self-sharpening ability
2 - J. Stubberfield, N. J. Lynch & I. Wallis, "Comparison of unitary and jacketed rod penetration into semi-infinte and oblique plate targets at system equivalent velocities", International Symposium on Ballistics

The drawbacks of front-mounted engines in modern main battle tanks

The Merkava series of main battle tanks (MBTs) is currently the only real MBT with a front-mounted engine. On light tanks, armored personnel carriers (APCs), self-propelled guns (SPGs) and infantry fighting vehicles (IFVs) placing the engine infront of the crew compartment is a common design practice, but on main battle tanks this is a rarity.

The Merkava tanks with their front-mounted powerpacks are a modern oddity and rarity

The reason for this is that having a front-mounted engine comes with a rather huge number of drawbacks, compared to only a few advantages, which by most countries are not considered as mandatory improvments for a tank.

A front-mounted engine does have a number of drawbacks in regards to the tank's armor protection:

• A frontal engine reduces the space available for special armor  
• Modern composite armor is very bulky and requires a lot of space (more than 600 milimetres for the hull on modern tanks) in order to deal with all available threats; a powerpack is taking up a lot more length (about 1500 mm for the MT 883 engine), but increasing the length of the tank's hull is not desireable, as it has a huge number of drawbacks. In case of the Merkava tank, the frontal hull armor is thinner than that of a comparable MBT from another country. 
• It also increases hull height
• The height required for a seated driver (in a reclining position) is lower than the height required for a powerpack. In case of the German Leopard 2 MBT, the height at the start of the UFP (upper front plate) is about 1 metre above the ground. The height at the end of the UFP is about 1.522 metres above the ground, where the rear section of the hull where the powerpack is mounted, is located 1.774 metres above the ground: mounting the engine at the hull front would increase the height of the hull by 222 mm (or 272 mm if we include the difference in ground clearance between Leopard 2 hull front and rear). That's about half the size of the UFP!
• This also can lead to an increased turret height
• Due to the higher hull and the turret ring being moved backwards (in comparison to other tanks), the turret has to be higher, unless a lower range for gun depression and elevation is deemed as acceptable. If the turret was not taller, the gun would hit the UFP everytime the crew tries to depress the gun. In case of the Merkava reducing the gun depression was chosen, so that the Mark IV has only 7° gun depression instead of the approximately 10° reached by other tanks with manned turrets.   
• A front-mounted engines also means that more weight and volume of the special armor has to be utilized for reaching the same amount lateral protection
• In order to reach what is considered by tank manufacturers a decent level of protection for the crew, heavy ballistic skirts (with a thickness of 65 to 200 mm) are used on the frontal sections of the hull. Unlike the non-ballistic skirts, the heavy ballistic skirts consist of composite armor or ERA, and are designed to provide protection along the frontal 60° arc for the whole crew compartment. Due to placing the crew compartment of the tank behind the engine, a larger area of the sides needs to be protected by heavy ballistic skirts, which means (for a constant weight) that less armor can be utilized for the front.

Additional length for the heavy ballistic skirts (red) and base armor (yellow) are needed on the Merkava to protect the crew (teal)

Compared to a Leopard 2, the Merkava has about 100 mm less ground clearance and an about 200 mm greater height to the turret roof. The height to the top of the UFP is about 300 mm larger on the Merkava, as measured on different photographs of the Merkava II and Merkava III.

This drawing of a M1 Abrams hull shows how the hull front is not as tall as the rear and thus the frontal profile can be kept smaller

While a powerpack and also fuel tanks will offer some amount of protection against impacting projectiles (although less than actual armor will - both per thickness and per weight), it should be taken into account that this is a different type of protection:
Once the powerpack is damaged from a projectile or the fuel systems are ignited, the tank will become imobile and won't be able to participate in any further combat actions. Instead of the crew dying, the damaged tank will be a mobility kill or a mission kill. This also means however that other parts of the forces have to secure the damaged tank and guard it until reinforcements or combat engineers have arrived - because otherwise the damaged tank will turn very easily into a total loss, when enemy forces attack it. In other words: a front-mounted engine can only provide crew protection, the tank as a system however will be even more susceptible to damage.
Actual armor on the other hand does not only crew protection, but also system protection. If an impacting projectile is stopped by the special armor, it won't be able to damage the internal components of the tank. The tank as a system stays intact and can still participate in combat.

The lower front plate of the Merkava is protected by very thin armor only

Furthermore a number of negative performance features are interwoven with the decision to utilize a front-mounted powerpack in a modern tank. The driver's vision in close proximity is reduced, because he is located further away from the frontal edge of the hull and because the hull is taller. The static track tension will be higher. The drive sprokets located at the front are more exposed to rocks and other obstacles, which means at higher speeds the drive sprockets can be hit and will be damaged easier. Also the air-intakes and/or the exhaust vents have to be located at the sides of the hull or at the front, which will get clogged on dusty/sandy terrain more easily. 

In case of infantry fighting vehicles and armored personnel carries, placing the powerpack in the front of the vehicle does offer a great benefit: a rear ramp/door - the infantry squad can enter and disembark from the vehicle without being exposed to enemy fire, while the thicker frontal armor of the vehicle can face the enemy. As there are currently not many purpose-built light tanks, most light tank designs are based on IFVs in order to keep costs down. Here placing the engine at the front means just saving costs compared to redesigning the hull and vehicle.

Like most modern light tanks, the CV90-120 just mounts a turret on the IFV chassis

For self-propelled guns placing the engine in the front of the vehicle is benefical, because the vehicle have a huge demand for ammunition (so a rear door for ammo replenishment is needed) and due to the extreme length of the gun barrels, which requires the turret to be placed further away from the front to reduce gun overhang and add stability while firing.

For the Merkava series the front-mounted engine made sense, when we look at it's history. Israel lacked modern armor technology and thus relied on spaced armor only. The armor layout of the Merkava I and II is optimized for hull-down combat from static positions, which was the most common type of operation for tanks during most of the Israel-Arab conflicts of the past, such as the Yom-Kippur War and the Six Days War. The weaker lower hull of the Merkava would be hidden behind the terrain or prepared (concrete reinforced) positions, so that the hitting them would not be possible. The lack of (bulky) composite armor also meant that no system protection is lost compared to a tank with homogenous or spaced armor and rear-mounted engine.

The frontal hull armor of a Merkava I or II tank. All armor is placed in front of the engine!

The later models of the Merkava series however suffer unnecessary weaknesses from their inheritance. At a 60-65 metric tons weight, but a larger physical size and a much larger armored surface (more armor required for the frontal surface, for the sides, the rear, the roof, aswell as for the mine-protection), the Merkava tanks should not be expected to be as well armored as their European or some of their Asian competitors.

Object 299 prototype tank - the front-mounted engine had a huge impact on mobility and maximum armor thickness.

All major tank building nations have experimented with tanks, which had their engines mounted in the front or in the center section of the tank. None of these experiments resulted in the adoption or creation of a new MBT with front-mounted powerpack.