As early as January 1940, Roebling had prepared preliminary sketches of an LVT with a gun turret to provide fire support to the landing waves. The concept languished until June 1941, when USMC recommended development of an LVT armed with a 37mm gun and three machine guns and armored against 0.50 (12.7mm) machine gun fire. Development was slow and ultimately involved a complete redesign of the LVT, the LVT-2 Buffalo. Armored versions were introduced as well as fire support versions, dubbed "Amtanks", which were fitted with turrets from Stuart series light tanks (LVT(A)-1) and Howitzer Motor Carriage M8s (LVT(A)-4).