Tanks in World War I
The continued need for four men to drive the tank was solved with the Mark V which used Wilson's epicyclic gearing in 1918. Also in 1918 the French produced the Renault FT, the result of a co-operation between Estienne and Louis Renault. As mentioned before, it had the innovative turret position, and was operated by two men. At just 8 tons it was half the weight of the Medium A "Whippet" but the version with the cannon had more firepower. It was conceived for mass production, and the FT became the most produced tank of World War I by a wide margin, with over 3,000 delivered to the French Army. Large numbers were used by the Americans and several were also lent to the British.
Tank destroyer battalion (United States)
The first nine units were deployed during the Louisiana Maneuvers of 1941, equipped with towed 37 mm anti-tank guns (the largest gun that could be towed by a jeep) and 75 mm guns mounted on half-tracks (the M3 Gun Motor Carriage), and again in the Carolinas maneuvers that November. Their employment was judged a success—though not without some disgruntled voices in the armored branch arguing that the umpires had rigged the results—and on 27 November, Marshall ordered the establishment of a tank destroyer Tactical Firing Center at Fort Hood, Texas, under Bruce, and the activation of 53 new anti-tank battalions under the command of General Headquarters. The term "tank destroyer" was used from this point on, as it was seen as a more psychologically powerful term. On 3 December, all existing anti-tank battalions were reassigned to General Headquarters and converted to tank destroyer battalions.
The new tank destroyer doctrine was formally stated in Field Manual 18-5, "Tactical Employment, tank destroyer Unit", in June 1942. It laid down a focused doctrine—"There is but one objective of tank destroyer units… the destruction of hostile tanks"—and repeatedly emphasized an offensive, vigorous spirit. Tank destroyer units were expected to be employed as complete battalions, held in reserve and committed at critical points, rather than parceled out as small defensive strongpoints. The emphasis was heavy on mobility, and the ability to outmaneuver the attacking armor; this would feed into vehicle design, and cause the speed of a vehicle to be prioritized over survivability.