No 5 Mk 1 Mills Bomb
Developed in 1915 by William Mills, a Birmingham engineer, the Mills Bomb had a central spring-loaded firing-pin and spring-loaded lever locked by a pin. Originally it had a 7 second fuse which required that the bomber held the bomb for 3 seconds after ignition otherwise the enemy could throw it back before it exploded. In the newer models once the Mills Bomb was in the air, the lever flew up and released the striker, which ignited a four-second time fuse, allowing the thrower to take cover before it exploded.
The Mills grenade became very popular with British troops and remained in short supply until the end of 1916. By the time the Armistice was signed, more than 33 million Mills Bombs had been issued.