Mills bomb is the popular name for a series of prominent British hand grenades

They were the first modern fragmentation grenades used by the British Army & saw widespread use in WWI

William Mills, a hand grenade designer from Sunderland, patented, developed & manufactured the "Mills bomb" at the Mills Munition Factory in Birmingham, in 1915

The Mills bomb was inspired by an earlier design by Belgian captain Leon Roland

Roland & Mills were later engaged in a patent lawsuit

The Mills was adopted by the British Army as its standard hand grenade in 1915 & designated the No. 5

It underwent numerous modifications

The No. 23 was a variant of the No. 5 with a rodded base plug which allowed it to be fired from a rifle

This concept evolved further with the No. 36 variant with a detachable base plate to allow use with a rifle discharger cup

The final variation of the Mills bomb, the No. 36M, was specially designed & waterproofed with shellac for use initially in the hot climate of Mesopotamia in 1917, but remained in production for many years

The Mills was a classic design a grooved cast iron "pineapple" with a central striker held by a close hand lever & secured with a pin

According to Mills's notes, the casing was grooved to make it easier to grip & not as an aid to fragmentation, & in practice it has been demonstrated that it does not shatter along the segmented lines

The Mills was a defensive grenade: after throwing the user had to take cover immediately

A competent thrower could manage 15 metres with reasonable accuracy, but the grenade could throw lethal fragments farther than this

The British Home Guard were instructed that the throwing range of the No. 36 was about 30 yards with a danger area of about 100 yds

At first the grenade was fitted with a 7-second fuse, but during combat in the Battle of France in 1940 this delay proved to be too long, giving defenders time to escape the explosion, or even to throw the grenade back, & was reduced to 4 seconds.