The idea for the 'exploding' rat - now immortalised as part of the SOE legend - was developed in 1941. The aim was to blow up the enemy's boilers by lying the rat on the coal beside the boiler, with the fuse being lit when the rat was shovelled into the fire. They were never used, as the first consignment was seized by the Germans and the secret was blown.
The Germans were fascinated by the idea, however, and the rats were exhibited at the top military schools. Indeed, the SOE files show that the Germans actually organised searches for these rodent explosives. The source of the dead rats was a London supplier, who was under the mistaken belief that it was for London University.