Special treatment steel
Special treatment steel (STS), also known as protective deck plate, was a type of warship armor developed by Carnegie Steel around 1910. History STS is a homogeneous Krupp-type steel developed around 1910. The development of such homogeneous steel resulted from testing which showed that face-hardened armor was less effective against high-obliquity glancing impacts. Around 1910, Carnegie Steel developed a new nickel-chrome-vanadium alloy-steel that offers improved protection over the prior nickel steel armor, though vanadium was no longer used after 1914. This alloy-steel became known as "Special Treatment Steel (STS)"; it became the U.S. Navy Bureau of Construction and Repair (later Bureau of Ships) standard form of high-percentage nickel steel used on all portions of a warship needing homogeneous direct impact protection armor. STS was used as homogeneous armor that was less than thick; homogeneous armor for gun mounts and conning towers, where the thicknesses were considerably greater, used Bureau of Ordnance Class "B" armor which had similar protective properties as STS. Somewhat more ductile than the average for any similar armor, even Krupp's post-World War I "Wotan weich" armor, STS could be used as structural steel, whereas traditional armor plate was entirely deadweight. STS was expensive, but the United States