Making Mills Bombs

The No.36 or Mills Bomb was one of the longest serving grenades, developed during the First World War it originated from a Belgian design by Albert Dewandre and Capitaine Léon Roland. It was improved by a British industrialist, William Mills, who owned several metal forging factories.

A No.36 Grenade (Matthew Moss)

It entered service in late 1915 as the No.5 Mk1 and continued to be improved during the war with several iterations before it finally became the No.36M Mk1. We’ll look at the Mills bombs development more closely in a future video/article – today, with the help of some 1940s newsreels from New Zealand we’re going to look at how they were manufactured. While the newsreel doesn’t state the factories featured they were made by a number of factories including Anderson Engineering in Christchurch (these were marked with an “A” below the filler plug), Booth Mcdonald, of Christchurch (marked BM), Scott Brothers, also of Christchurch (marked SB), and Mason & Porter, of Mt Wellington, in Ackland (marked MP).

William Mills’ 1916 Patent for the grenade.

In the first newsreel, courtesy of Archives New Zealand (Weekly Review No. 70 (1943)), we see No.36 grenades being cast – the newsreel takes a slightly humorous approach of describing the process as a recipe – making ‘pineapples’ – a slang name by which grenades were sometime’s known. The factory is using the sand casting method with a pattern pressed into the sand and then removed. The two halves of the grenade’s body are pressed into sand, a pressed sand core could then be placed inside which would allow the grenade’s body to be poured hollow to allow room for explosives and detonator. If we again pause here we can see a machinist is centring and counter-sinking the filling hole’s first thread for its plug.

Cast grenade bodies ready for filling (Archives New Zealand)

The footage includes a brief shot we see a woman factory worker drilling out the top of the grenade’s body and perhaps de-burring the side of the safety lever holder. In the next shot we see more machinists at work with one lady linishing the body of the grenade, removing imperfections from the casting on a grinder or polishing wheel and in the background some women a working on milling machines or drill presses. 

Women factory workers linishing the grenade body castings (Archives New Zealand)

At the very end of the film we can see the grenade bodies are stacked ready for the next phase of production. Sadly, we don’t see the threading of the filling hole or base in this film nor the painting or filling of the grenades.

In the second newsreel (Weekly Review No. 63 (1942)), however, which celebrates the production of 1 million grenades, we do seem more of the production process. In this short segment we see how the grenades are filled and how they work. We see the cast bodies of the grenades being transported on a conveyor after being shellacked to keep moisture out. If we pause here we can see this worker packing a case with “gascheck” discs and fuses.

Loading grenades, fuses and gas checks into a transit case (Archives New Zealand)

The gas check disc and a 7 second fuse was used when the grenade was being fired from a rifle’s cup discharger, while a 4 second fuse was favoured when throwing by hand. In this final clip we see the internals of a grenade – which was filled with just over 2oz of explosive through the round filling-hole (on the side opposite the safety lever) which was then screw plugged. The newsreel then concludes the grenade segment by showing the striker spring inside being compressed and a No.27 Detonator, with fuse, being inserted into the sectioned grenade.

We’ll examine more British grenades, including the No.36 in future videos and articles.


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Bibliography:

Weekly Review No. 63 (1942)

Weekly Review No. 70 (1943)

W. Mills, ‘Grenade and Other Like Apparatus’, 4 Apr. 1916, US Patent #1178092, (source)

NZ Mills Grenades, Lexpev.nl, (source)

No.36 Mk1 Grenades, MillsGrenades, (source)

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