One prime example are the armor estimations (called Armor Basics) from Paul Lakowski from SteelBeasts, which have found their way to Scribd. These values were reposted on J. Collin's table-top war gaming reference website (link death, use link with web archive to visit the site) and from their have found their way to Fabian Prado's The Armor Site! and even some of the worse written Wikipedia articles (yes, this is the Abrams' article).
Why are these values wrong and outdated?First of all, they are based on a faulty conception of modern armor design. The author believed that all Western composite armor was based on a relatively simple layout, consisting of steel plates, between which layers of ceramic and kevlar were sandwiched. In the same way Chobham armor was described during the 1980s.
We know however from literature, declassified documents from the development of Chobham armor, and from photographs of damaged tanks, that this is not the case. So the basic idea of his armor estimations is already wrong.
|Damaged Merkava IV tank - note that this is not "kevlar + ceramic"|
However we do know that this is not the case, because on different Leopard 2 tanks people have used simple measure bands to measure the armor thickness.
It happens that the Leopard 2 has only about 860 milimetres of frontal armor, with an 420 milimetres thick gun shield (behind this is still a lot of steel from the gun trunion and the gun mount). So the thickness values to calculate the armor protection levels are also false.
|Leopard 2 frontal turret armor - 800 mm without backplate!|
Calculating the density is a good way to estimate the armor protection of a tank, when you have a basic idea about how modern armor works. But when you already have wrong values for armor thickness, it is obvious that you will end up with either a higher or lower density than the real value.
In case of the Leopard 2, which has approximately 20% - 40% thinner armor than estimated, the density will be a lot lower than it should be. Hence in Armor Basics the Leopard 2 turret armor consists of "2/3 aluminum + SHS + AD-85 + Rubber", i.e. it is made mostly out of aluminium.
In reality however Paul-Werner Krapke, project manager of the Leopard 2 development, describes the armor to utilize different steel alloys of high hardness and ductility in combination with non-metallic and elastic materials, which by my understanding suggests NERA.