In the Iraq war, it was found that the M-1 tank was vulnerable to some attacks from the rear. This is nothing new. Since World War II, tanks have been built with their thickest armor in the front, and tactics were based on trying to keep the front of your tanks facing the enemy weapons. But in any battlefield, things get mixed up. In Iraq, there were instances where M-2 Bradley infantry vehicles got a shot at Iraqi T-72 tank with its 25mm auto-cannon. The shells fired (25mm armor-piercing, fin-stabilized discarding sabot using a depleted uranium penetrator) appeared to penetrate the side of the T-72 turrets and cause tanks to start burning. The penetration of that particular 25mm shell is classified, but if it's over 50mm, there's no reason why it would not have gone through the thin side armor of the T-72 turret. While no M-2 crew wants to try it, it is felt that in a head on, short range engagement, the 25mm auto-cannon, firing on full automatic (200 rounds a minute, or 3-4 a second), might disable a T-72 if it could get a few seconds of fire on the T-72. While the armor could not be penetrated, the main gun tube and fire control equipment can be disabled. Again, no one wants to try this for real. Better to sneak around and get a side shot.