This is my homage (reproduction) of an SOE 'Rats, Explosive'. As you can see there was obviously a little bit of artistic licence used when the diagram was drawn, either that or they had very big rats in WW2 (my rat is over 8" long excluding the tail!).
The Switch No.10 commonly referred to as the a 'time-pencil fuse / pencil time fuse / P.T.F' is an original and is marked red so it has a 30 minute delay. I have crudely mocked up a standard No.6 primer, however, as I cannot find what an original looks like it is probably totally wrong - if anybody has an image please show. I have used green plasticine for the plastic explosive as it closely resembles Nobel 808 / Explosive 808 which was the used a lot by the British, especially early in the war (I could have used cerise plasticine as it was used for demonstrations to replace actual plastic explosives).
The history of the exploding rat:
The idea for the exploding rat was developed in 1941. The plan was that when the dead rat was discovered in the boiler room of a locomotive, factory, power station, or similar installation, the stoker tending the boiler would dispose of it by shoveling it into the furnace, causing the booby trapped rat to explode. A rat could contain only a small amount of explosive; however, a penetration of a highly pressurized steam boiler could trigger a devastating boiler explosion. A rat bomb could also be set with a delayed fuse (as per my reproduction)
The explosive rats never saw use, as the first shipment was intercepted by the Germans and the SOE plan was dropped. The Germans were fascinated by the idea, however, and the rats were exhibited at top military schools. The SOE files show that the Germans actually organised searches for these rodent explosives concluding that; "The trouble caused to them was a much greater success to us than if the rats had actually been used."
The source of the dead rats was a London supplier, who was under the mistaken belief that it was for London University!