performance dropped off as range increased due to poor aerodynamics. The M72 was replaced by the 6.63 kg (14.62 lb) M61 armor-piercing ballistic capped high explosive with tracer (APCBC-HE-T) shell. The blunt armor-piercing cap, made of a softer metal, helped to prevent shell shatter at higher velocities and against sloped and face-hardened armor. The aerodynamic ballistic cap acted as a windscreen and improved ballistic performance, maintained velocity, and hence increased penetration at longer ranges. Once the projectile had penetrated the target, a small explosive charge contained in a cavity at the base of the shell would detonate, shattering the shell and increasing damage inside the enemy vehicle. The tracer helped in the aiming of a second shot. In practice, the majority of M61 rounds were shipped without the explosive filler. The M61A1 used an improved method of attaching the ballistic cap to the shell. The M61 had a muzzle velocity of 617 m/s (2024.28 ft/s) and was credited with the ability to penetrate of rolled homogeneous armor plate at 0° from vertical at 500 yards range, which was a quite acceptable performance by the standards of 1942. This ammunition type proved lethal to the Panzer III and IV (up to Ausf. F2), as these tanks were protected by a maximum of 50 mm of face-hardened armor with little slope, which the 75 mm M3 with M61 was capable of penetrating from at least 1,500 m. However, in March 1942, the Germans introduced the Ausf. G version of the Panzer IV, which was armed with the 48-caliber long KwK 40 gun, and had frontal hull armour increased to 80 mm - however, its turret and gun mantlet retained their 50 mm thickness. This was somewhat compensated by the M4 Sherman's improved armor over the earlier M3 Lee making up for the 75mm M3's diminishing battlefield dominance; Wa Pruef 1 estimated that the M4's standard 56º-angled glacis was impenetrable to the KwK 40 when standing at a 30-degree side angle, while the 75 mm M3 could penetrate the Ausf G's hull from 100 m in the same situation. British tanks in the early years of World War II relied on high-velocity, smaller-calibre anti-tank guns, such as the 40 mm calibre Ordnance QF 2 pounder and, later, 57 mm calibre Ordnance QF 6 pounder, for their primary armament. As tank guns, these had the great disadvantage of either not having a truly effective