Mills bomb

A Mills bomb is the popular name for a series of prominent British hand grenades, the first modern fragmentation grenades used by the British Army and saw widespread use during the First World War. 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.

The heavy segmented bodies of "pineapple" type grenades result in an unpredictable pattern of fragmentation. After the Second World War Britain adopted grenades that contained segmented coiled wire in smooth metal casings. The No. 36M Mk.I remained the standard grenade of the British Armed Forces and was manufactured in the UK until 1972, when it was completely replaced by the L2 series. The 36M remained in service in some parts of the world such as India and Pakistan, where it was manufactured until the early 1980s. Mills bombs were still being used in combat as recently as 2004 e.g. the incident which killed US Marine Jason Dunham and wounded two of his comrades.


 * The No.5 Mk. 1 was the first version. The explosive filler was loaded through a small circular plug on the upper half, the detonator assembly was loaded through the bottom through the baseplug, and the pull-ring striker was screwed in to the fuse well at the top. The lever was protected by metal "ears" flanking the top that could be used to locate it in darkness. It was first issued in May, 1915 but wasn't in general issue until mass production caught up a year later in 1916. The Mk. 2 had a redesigned stronger safety lever.
 * The No.23, the rifle-grenade model, first appeared in 1917. The No. 23 Mk. 1 had a redesigned, narrower baseplug that was centrally threaded underneath so it could attach the rifle rod. The Mk. 2 and Mk. 3 were product-improved versions designed to make it cheaper and easier to produce.
 * The improved No.36 Mk. 1 was first introduced in May, 1918. It was wider in the middle, had larger lever "ears", and had an optional gas-check disk to allow it to be launched out of a blank-propelled cup-discharger. The shellac-coated "Mesopotamian" variant (No. 36M) was designed to keep moisture and humidity out of the detonator's fuse. The No.36M Mk. 1 was the British army's standard hand-grenade from the 1930s to the 1970s.