Mk-II A1 Grenade
The standard fragmentation grenade used by American soldiers in World War II was the Mk-II A1, sometimes referred to as a "pineapple" due to its shape.
The grenade was armed by holding down the handle and pulling a metal ring which was attached to a safety pin. Although armed, the grenade would not detonate until the handle was released and a striker impacted the grenade's fuse. The fuse was designed to detonate after 5 seconds, but this time could vary considerably.
Notes
As is demonstrated in the film, one of the potentially dangerous aspects of using grenades—both American and German—are the variable lengths of the fuses. If a grenade is thrown too soon it is possible (if unlikely) for the enemy to throw the grenade back at its thrower. If the grenade is held too long ("cooking" the grenade), in order to prevent such a possibility, it is possible for the grenade to detonate in the thrower's hand, or to explode harmlessly in the air while on its way to its target. One effective use of a cooked grenade—an airburst—can result in the grenade exploding above its target, which is particularly deadly.