Mills Bomb

Mills bomb
Mills bombs. From left to right : N°5, N°23, N°36.
Type	Hand grenade
Place of origin	United Kingdom
Service history
In service	1915–1980s
Production history
Designed	1915
No. built	70 million +
Variants	No. 5, No. 23, No. 36, No. 36M
Specifications
Weight	765 g (1 lb 11.0 oz)
Length	95.2mm
Diameter	61 mm (2.4 in)
Filling	Baratol
Detonation mechanism	Percussion cap and time delay fuse: 7 seconds, later reduced to 4

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 and saw widespread use in WWI.

William Mills, a hand grenade designer from Sunderland, patented, developed and manufactured the "Mills bomb" at the Mills Munition Factory in Birmingham, England, in 1915. The Mills bomb was inspired by an earlier design by Belgian captain Leon Roland. Roland and Mills were later engaged in a patent lawsuit. The Mills bomb was adopted by the British Army as its standard hand grenade in 1915, and designated the No. 5.

The Mills bomb 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, a 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 and waterproofed with shellac for use initially in the hot climate of Mesopotamia in 1917, but remained in production for many years. By 1918 the No. 5 and No. 23 were declared obsolete and the No. 36 (but not the 36M) followed in 1932.

The Mills was a classic design; a grooved cast iron "pineapple" with a central striker held by a close hand lever and secured with a pin. According to Mills's notes, the casing was grooved to make it easier to grip and not as an aid to fragmentation, and 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 (49 feet) 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 seven-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, and was reduced to four seconds.