pre-arranged firing positions to best advantage. Flanking fire by TDs was emphasized, both to penetrate thinner enemy side armour, and to reduce the likelihood of accurate enemy return fire. All American tank destroyers were officially known by exactly the same collective term used for American self-propelled artillery ordnance, "gun motor carriage". The designs were intended to be very mobile and heavily armed. Most of the tank-hull based designs used special open-topped turrets of a differing design from the original tank it was based on, which was meant to both save weight and to accommodate a larger gun. The earliest expedient design was an M3 Half-track mounting an 75 mm Field Gun M1897 on M2 Carriage in a limited-traverse mount, and called the 75 mm Gun Motor Carriage M3. Another, considerably less successful, early design mounted a 37-mm anti-tank gun in the bed of a Dodge 3/4-ton truck—the 37-mm GMC M6. By far the most common US design, and the first that was fully tracked and turreted (which became the American hallmark of World War II "tank destroyer" design) was the 3in Gun Motor Carriage M10, later supplemented by the 90 mm Gun Motor Carriage M36—both based on the M4 Sherman hull and powertrain—and the 76 mm Gun Motor Carriage M18 (Hellcat), based on a unique hull and powertrain design, with a slight visual resemblance to what was used for the later M24 Chaffee light tank. The M18 came closest to the US ideal; the vehicle was very fast, small, and mounted a gun in a roofless open turret. The M36 Jackson GMC possessed the only American-origin operational gun that could rival the vaunted 88 mm German anti-tank ordnance, the 90 mm M3 gun, and the M36 remained in service well after World War II. The only dedicated American casemate hull design fighting vehicle of any type built during the war, that resembled the German and Soviet tank destroyers in hull and general gun mounting design, was the experimental T28 Super Heavy Tank, which mounted a 105 mm T5E1 long-barrel cannon, which had a maximum firing range of 12 miles (20 km), and was originally designed as a self-propelled assault gun to breach Germany's Siegfried Line defenses. Of these tank destroyers, only the gun of the M36 proved effective against the frontal armour of Germans' larger armored vehicles at long range. The open top and light armour made these tank destroyers