However in many cases spaced armor is designed to deal with armor-piercing ammunitions such as AP and APDS rounds mainly. This already started during WW2, when spaced armor was first introduced on German Panzerkampfwagen III and IV tanks. The Panzerkampfwagen III Ausf. L received spaced frontal armor by adding a 20 mm steel plate at the hull superstructure and the gun mantlet. This first steel layer was designed to damage or shatter the caps of APCBC ammunition, so that the face-hardned main armor was more effective.
|A Panzerkampfwagen III with spaced armor (note the brackets and the spaced 20 mm plate)
|Panzerkampfwagen IV Ausf. H with spaced armor against anti-tank rifle ammunition
While not adopted on follow-up production tanks in the late 1940s and 1950s, spaced armor was still tested and reintroduced to modern tank design in the late 1960s and early 1970s.
In an attempt of accessing the usefullness of shaped charges against future heavy tanks, the British army decided to trial spaced armor as upgrade option for the Conqueror heavy tank.
|Conqueror fitted with spaced armor
Meanwhile Germany and the United States were together working on a new main battle tank, known as the MBT-70. The MBT-70 was fitted with spaced armor at the hull front and turret, which used a thicker and harder outer plate than the previously mentioned designs. According to R. M. Ogorkiewicz, the outer plate had a thickness of 40 mm and had a hardness of over 500 BHN, or about twice as much as used on the then-used cast steel turrets. The main armor had greater thickness, but only medium hardness. The outer plate served as disruptor - it's main goal was to shatter or break the impacting penetrator instead of slowing it down by any major amount. This was extremely effective until the late 1970s and early 1980s, because most penetrators used brittle tungsten-carbide cores or steel cores. Supposedly against such ammunition, spaced steel armor utilizing steel plates of different hardness can increase the protection by up to 50% compared to homogenous steel of the same weight. At least it has been claimed by W. J. Spielberger, that the MBT-70 was protected against 105 mm APDS ammunition fired from 800 m distance, while the same ammunition was able to penetrate the 254 mm thick turret of the M60A1 tank even at 1,500 m range - the MBT-70 was designed to weigh 46 metric tons, but in reality ended up 48 metric tons (second generation prototypes), whereas the M60A1 weighs 52 metric tons!
This armor design went - after being used on the Keiler and early Leopard 2 tanks - into series production with the German Leopard 1A3 tank in 1973.
|The cut-out section of a Leopard 1 turret side wall shows the spaced armor.
The list of modern armored vehicles utilizing spaced armor for protection against AP ammunition is very large and includes vehicles such as the Boxer, several armor upgrades for BTR and BMP, some versions of the Stryker, many different versions of the M113 and the AAV-7.
|Ukrainian BTR with spaced armor for protection against HMG rounds.
Spaced armor allows achieving a greater level of armor protection per weight, but it does increase the physical size of the vehicle at the same time.