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British No.24 Mk.II Rod Grenade
The British No.35 Mk.I is pretty much the end of the line in  Rod Grenade development. While two more rifle grenades were to be developed... the No. 39 "Stewart" (An experiment with a different impact fuze.) and the No.44 Anti-Tank (basically a very larger H.E. Warhead), this was pretty much as far as the concept was to go.  It was around 1917, the Mills No.36 cup launcher was in development and the Germans had fielded their own cup launched grenade system based on the French V.B. design.
As with the others of this type, the basic principal hadn't changed... a weighted firing pin restrained in flight by a creep spring, locked before firing by a pair of restraining bolts, held in place by a safety collar. The trends observed in the No.24 continued with ever more simplified design feature for ease of manufacturing and reduced material requirements.

Inset is the parts detail from the No.24 grenade for reference. Note the striker geometry has changed. This allowed the base plug to be reduced in length by half, saving that always most strategic of war materials, copper. The set-back safety collar is a bit smaller and the safety pin now goes thought that and the base piece. The detonator housing is also simplified to a zinc and copper swaged assembly.

The parts count here is 12, down from 15 with very few precision machined parts.

The body is marked with:"No.35" E" T, and the top ring and plunger are stamped G.T.L.. 

The red color is probably copied from the French (and Germans) signifying a practice round. The common practice was to use live fuze/detonator assemblies without the H.E. filler. Often this meant the grenade body would still burst during use, but there would be no significant fragmentation effect. Seems the Germans were the first to make practice grenades with holes in the bodies to vent the pressure. It seems odd that it took the rest of the world until W.W.II to figure that his was a good idea as well.

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