Aston House was a large, secluded country house surrounded by of parkland. The house had been acquired by the Secret Intelligence Service (SIS) in 1939. The SIS, a secret branch of the Foreign Office, then handed the house over to SOE for whom it became known as Station XII. Aston House was used to produce and package special weapons and to train SOE agents in their use. The station had a high wire fence and many security measures. When Clarke first arrived at Aston House he was kept waiting at a guard post, but after a few minutes he slipped past the security measures and got into the house and into the presence of the station's commandant, Arthur Langley. Langley did not take kindly to his initiative and forbade Clarke to enter the house or to be served with meals – this continued until Langley was replaced some months later by Captain Leslie John Cardew-Wood (generally known as John Wood). A wide range of munitions, including the limpet mine and the spigot gun, were produced at Aston House. Significant development work went on including some early work on shaped charges. Having resigned from his job at the Admiralty, Clarke joined the Army and was taken on by Wood to work at Aston House, where he was put in charge of training SOE saboteurs. Clarke developed a weapon that he called the spigot gun. It was a type of spigot mortar that propelled a projectile consisting of a bomb about in diameter containing of high explosives and a finless tail tube containing a propelling charge similar to a shotgun cartridge. The bomb had a thin front that collapsed when it struck a target, thereby placing the explosive in intimate contact with the target immediately prior to detonation; the bomb could penetrate up to 50 mm of armour. The hollow tail was placed over a spigot so that when the propelling charge was fired, the projectile would fly off; this sudden acceleration also armed the contact detonator. As soon as the projectile had left the spigot, a plug would block the tail tube, greatly reducing the flash and noise of the discharge. Simple, quiet, and easily portable, the spigot gun was an ideal weapon for the saboteur and it was thought very suitable for jungle warfare. The most widely used version of the spigot gun was the "tree spigot gun". This had its spigot mounted on a ball and socket joint attached to a large wood screw. A pair of handles were provided to turn the screw so that it could be secured in a tree or other suitable wooden support; one of the handles had a chisel-shaped end for removing bark from trees.