An anti-tank grenade is a specialized hand-thrown grenade used to defeat armored targets. Although their inherently short range limits the usefulness of grenades, troops can lie in ambush or maneuver under cover to exploit the limited outward visibility of the crew in a target vehicle. Hand launched anti-tank grenades became redundant with the introduction of standoff rocket propelled grenades and man-portable anti-tank systems. Grenades were first used against armored vehicles during World War I, but it wasn't until World War II when more effective shaped charge anti-tank grenades were produced. AT grenades are unable to penetrate the armor of modern tanks, but may still damage lighter vehicles. The first anti-tank grenades were improvised devices. During World War I the Germans were the first to come up with an improvised anti-tank grenade by taking their regular "potato masher" stick grenade and taping two or three more high explosive heads to create one larger grenade. In combat, after arming, the grenade was thrown on top of the slowly advancing tank where the armor was thin. The destructive properties of the stick grenade relied on its explosive payload, rather than the fragmentation effect, which was advantageous against hard targets. During World War II, various nations made improvised anti-tank grenades by putting a number of defensive high explosive grenades into a sandbag. Due to their weight, these were normally thrown from very close range or directly placed in vulnerable spots onto an enemy vehicle. Another method used by the British Home Guard in 1940 was to place dynamite or some other high explosive in a thick sock and cover the lower part with axle grease and then place the grease covered part in a suitable size tin can. The sock was pulled out, the fuse lit and the sock thrown against the side of the tank turret in the hope it would stick until the explosion. If successful, it caused internal spalling of the armor plate, killing or injuring the tank crew inside.