Allied Tank Guns: The American M1 and the British QF 17-Pounder Now we can move on to the Allied tank weapons of World War II. The Allies were not very strong when it comes to steel warfare. They relied on a lot of units that would out flank the Germans and hit them from the tanks weaker points. The British did have a solution and they called it the "Tiger Killer". As previously stated, the Tiger I was nearly impenetrable when it came to the Allied tanks. The M4 Sherman tank could not get penetrate with its weak M1 cannon. The British decided to mount their own 17-Pounder cannon on an M4 Sherman and this changed how the Allies fought the war of armor. First we will start of with the American M1 cannon. Pictured below is the 76mm M1 cannon that is mounted on an M4 Sherman. The M1 cannon was actually an improvement from the earlier M3 75mm cannon. The M1 was capable of taking out lightly armored targets such as the Panzer IV's. But when Nazi Germany introduced the Tiger I, everything changed. Relative to the German Tiger I's and Tiger II's, The M1 cannon was not very impressive. The only advantage that it had was that it was mounted on a reliable, fast tank that could easily maneuver around the enemy and strike. Now we will go into the physics of the M1 cannon. APBC:                 The M1 cannon had the M62 shell as their main armament. It had a mass of 7 kg with 0.065 kg of explosive filler. This totals up to 7.065 kg of projectile. If you remember from the Tiger I, it's APBC round had a much higher mass, coming in at 10.20 kg. The velocity of the projectile didn't help so much either. It only came out of the barrel going 790 m/s. Using the kinetic energy equation, we can see that the M1 APBC round only has 2,204,633 joules of energy. Not even close enough to penetrate a Tiger I from the front. This produces about 124mm of penetration. APCR:                 The true armor piercing round for the M1 cannon, the M79, is slightly better. This round travels the same speed as the APBC round, but also has more mass. It comes in at 11 kg and travels at 790 m/s. Determining kinetic energy, we find that it has 3,432,550 joules of energy, capable of penetrating 132mm of armor. Because of the poor statistics that were calculated above, the British didn't want to adopt the M4 Sherman with its M1 cannon. So they chose to do something a bit different and mount one of their guns on the M4 Sherman platform. Pictured below, this is the result: the Sherman Firefly. As you can see in the two different pictures, the Firefly has a much longer barrel, promoting muzzle velocity. This gun gave the Germans a surprise when they went up against it. Looking like the traditional American Sherman, the Germans had no idea that it was capable of taking out the mighty Tiger I. This is why the QF 17-Pounder cannon was a game changer. APBC:                 Being the most controversial round of the war, the APBC round that the QF 17-Pounder had was incredible. Having a mass of 7.71 kg and a speed of 884 m/s, It could penetrate 174mm of armor, easily destroying Tiger I tanks. The energy that it had was 3,012,512 joules. Because it was traveling very fast, it could penetrate German armor very well. There was no immediate need for an APCR round because the QF 17-Pounder APBC round did very well.