Grenades (small bombs thrown by hand) were first used in the 16th century. In the opening months of the First World War the British Army used Grenade No 1. This was a cast-iron canister on an 18 inch stick. Soldiers soon discovered that they were dangerous to use when in a front-line trench. There were several cases of soldiers being killed when the grenade hit the front of the trench.
In 1915, a grenade developed by William Mills, a Birmingham engineer, began to be used by British troops. The bomb had a central spring-loaded firing-pin and and spring-loaded lever locked by a pin. 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. When the grenade went off the cast-iron casing shattered producing a shower of metal fragments.
The grenade developed by Mills soon became very popular with British soldiers 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 to soldiers in the British Army.