As World War broadened across Europe following the events of 1914, design work began on a new standard hand grenade for the British Army in early 1915. Hand grenades proved worthy of the bloody fields of World War 1 where trench warfare dogged any advance. The grenade allowed the single operator the firepower to dislodge an entrenched foe by priming the explosive and lobbing it in the enemy's direction. The resulting explosion and subsequent spatter of steel fragments would kill, maim or shock the opponent into submission one way or another. However, all sides were keen on the use of the hand grenade and its appearance on these battlefields was as prevalent as the machine gun or rifle itself. The Mk I No. 5 became the standard hand grenade of the British Army shortly after it had cleared evaluations by May of 1915 and was thrust upon the enemies of the United Kingdom throughout World War 1. Sir William Mills (1856-1932, knighted in 1922) was credited with the development of the Mk I grenade and rightly bears his name as the "Mills Bomb".
Outwardly, the Mills Bomb showcased the classic "pineapple" grenade exterior which provided for a built-in hand grip of sorts. It was oblong in shape with a bulbous cylindrical body tapered at the ends. The safety pin was held on top and removed by way of a conventional metal ring and the hand level was snugly fitted against the grenade body. The grenade was first activated by the removing of the safety pin with a firm hold on the strike lever in place. The grenade could then be thrown against the enemy position to which the strike lever was jettisoned away during flight from the grenade body to activate the internal time-delayed fuse. The Mills Bomb weighed in at 765 grams and was over three inches tall. Its explosive component consisted of a Baratol filling which was made up of TNT, barium nitrate and wax. The detonation was handled by a time-delay fuse that ranged from seven seconds in original models to four seconds in the final production forms. Fragmentation direction was random and could affect the thrower's own position (blast radius of 35 meters being reported) so extreme care needed to be taken in its use. Interestingly, the grenades and their detonators were issued separately with assembly to be handled prior to combat.
The Mills Bomb existed in several notable forms beginning with the No. 5 model of 1915. This early form featured a time delay of seven seconds which proved to be too long, often having thrown grenade lobbed back at friendly positions. It was also designed for use with rifle muzzles for ranged firing. The No. 23 model was given a revised base plug for improved rifle firing. The No .36 model was the definitive grenade form that was issued with a base plate for increasingly improved rifle firing compatibility. The No. 36 was furthered into the No. 36M of 1917 which was coated in shellac for waterproofing and improved its battlefield life expectancy while the base plug was reinforced. Production was handled at British wartime facilities including the Mills Munition Factory out of Birmingham and overseas production was also noted across British interests worldwide. All told, some 70 million Mills Bombs were produced during the span of 1915 into the 1980s.
By the time of World War 2, the seven second fuse delay was standardized to four seconds which proved acceptable for combat operations thereafter. It was not until the 1970s that the Mills Bomb pineapple grenade family gave way to a more modernized L2 grenade form - a smooth-sided, oblong hand grenade developed in the United States (as the M26).
Amazingly, the Mills Bomb hand grenade saw extended use in the developing armies of the Middle East and Asia where the type can still be found in some number today.