75 Mm Gun M2/M3/M6 - History

History

The 75mm tank gun has its origins in the famous French Canon de 75 modèle 1897 field gun of World War I fame which was also adopted by the United States and used well into World War II as the 75mm M1897 field gun. Both the tank and field guns fired the same range of 75x350R ammunition. The primary round was the M48 High Explosive. This 6.76 kg (14.9 lb) round travelled at 625 m/s (2,050 ft/s) and contained 1.5 pounds of TNT filling and choice of Super Quick (SQ) or Delay (PD) with 0.05 or 0.15 seconds of delay fuse. SQ was the standard setting with PD used against structures, gun positions or lightly protected vehicles. The field gun origins of the ordnance and ammunition ensured that the M2/3/6 series HE round was highly effective for its caliber. The M48 was available in 2 versions, standard or supercharge which increased the propellent charge for greater muzzle velocity (1,885 ft/s (575 m/s) vs. 1,470 ft/s (450 m/s)) and range (2,300 yards greater).

Other important rounds fired by the 75mm tank guns were the T30 Canister shot for use against troops in the open at short range. This was essentially a giant shotgun shell full of large numbers of steel balls. Canister was used primarily in the Pacific. There was also a White Phosphorus (WP or "Willy Pete") round which proved highly effective in the Bocage fighting around Normandy. Finally there was the Armor-piercing for which 2 different rounds were provided.

The first armor-piercing round was the 18 lb (8.2 kg) M72 AP-T, a plain uncapped AP round whose performance dropped off as range increased. M72 was replaced by the 6.8 kg (15 lb) M61 and later the improved M61A1 APC Shell. This was actually a APC-HE-T or Armor Piercing Capped High Explosive Tracer type round which contained a tracer element so the gunner could follow the trajectory of the round to make corrections for the next shot if necessary. The cap improved ballistic performance and penetration. Once the projectile had penetrated the target a small explosive charge would detonate to increase damage inside the enemy vehicle. In practice the majority of M61 rounds were shipped without the explosive filler. M61 had a muzzle velocity of 620 m/s (2,030 ft/s) and was credited with the ability to penetrate 3.7 inches (94 mm) of armor plate at 500 yards range, which was a quite acceptable performance by the standards of 1942.

By July 1944 complaints started to pour in about the inadequate anti-tank performance of the M4 Medium tanks fitted with the 75mm M3 gun. During the breakout from Normandy American and British forces encountered the new generation of heavy German tanks and armored vehicles such as the Panther tank, Tiger I tank and Jagdpanzer IV tank destroyer in quantity for the first time. These vehicles had thick frontal armor that proved largely immune to the M61 projectiles fired by the M3 tank gun and severely tarnished the reputation of the M4 Medium tank. The western allies countered by equipping increasing numbers of M4 Medium tanks with the 76 mm gun M1 for the Americans and the Ordnance QF 17 pounder for the British. These guns offered much improved performance against tanks but because they fired High Explosive rounds that were inferior to those of the 75mm guns, the larger calibre guns never completely replaced the older models.

British tanks in the early years of World War II relied on high-velocity anti-tank guns such as the Ordnance QF 2 pounder and Ordnance QF 6 pounder for their primary armament. These guns had the great disadvantage for tank use of not having a truly effective High Explosive round or not even having the option of a HE round. The British after experiencing the effectiveness of the American 75mm tank guns in the infantry support role opted to adopt the American caliber and ammunition by the expedient of boring-out the 6 pounder tank gun to make the Ordnance QF 75 mm. By 1944 this had become the standard British tank gun equipping the Cromwell tank and Churchill tank for the campaigns in northwest Europe.