The Time Pencil A chemically activated time fuse designed to be connected to a detonator or short length of safety fuse. They are about the same size and shape as a pencil, hence the name. The Time Pencil like many other new weapons were issued to the Auxiliary Units at Coleshill before any other troops or covert units. The timer is started by crushing the copper section of the tube to break the phial of cupric chloride which then slowly eats through the wire holding back the striker. The striker then flies down the hollow centre of the detonator and hits the percussion cap at the other end of the detonator. No. 10 delay switches had delays ranging from 10 minutes to 24 hours and were accurate to within plus or minus 2 or 3 minutes in an hour's delay and plus or minus an hour in a 12-hour delay, though environmental conditions could affect this. The switches were typically issued in packs of 5, all the switches in a pack having the same delay. In use, two switches with the same delay (from different packs if possible) would be placed in the explosive charge in case one switch failed. Approximately 12 million pencil detonators were produced in Britain during the war. However, in recent years they have been superseded by electronic timers which are more accurate and provide much longer delay times. Interestingly, pencil detonators are by nature completely immune to detection or jamming via electronic countermeasures. For this reason they may still have applicability in special situations.
Operation Chariot In 1942 Royal Navy Commander R.E.D Ryder arrived at Coleshill House and the training team spent a whole weekend showing him how to use the time pencil. Ryder left on the Monday morning and the staff at Coleshill had no idea that he was on his way to lead the Naval force on “Operation Chariot”, the attack on the St.Nazaire dry-dock. St. Nazaire was targeted as the loss of its dry dock would force any large German warship in need of repairs, to return to home waters rather than seek safe haven in the Atlantic coast. Under the cover of what appeared merely to be a massive commando raid, the Royal Navy managed to ram the dockgates with a ship which was in fact a fuzed time bomb. The ship, Campbeltown, blew up and Ryder was awarded the Victoria Cross.
The Mysterious German U Boat Plot Coleshill was directly involved in the strange attack on a German U boat off the Shetland Islands. A Shetland farmer was busy during the lambing season when he heard a strange noise beneath a cliff edge. It was the humming of a German U-boat charging it’s batteries. It was reported through Scottish Command to Coleshill by a young man called Tim Iredale. Coleshill sent for Iredale and he spent the next week learning how to use time pencils, set plastic explosives and plant limpet mines. The woodland surroundings at Coleshill provided the training ground and he studied a scale model of the boat. He returned to the Shetlands and under the cover of darkness stripped off and entered the water with his time pencils and a limpet mine strapped to his chest. He reached the boat and placed the flat side of the mine against the boat just under the waterline. Just before dawn the U-boat submerged and departed, as it had done many times before. It was never seen again. German naval historians say this story could not have happened but the Coleshill Auxiliary Unit officers insist that this attack took place.
Usage in the 1944 plot to assassinate Hitler The briefcase bomb used in the July 20 plot used a captured British pencil detonator inserted into a block of British plastic explosives weighing approximately two pounds. The bomb was set to 30 minutes and detonated as planned, but Hitler survived with minor injuries. Stauffenberg could not prepare the second block, though. He got rid of it while driving through the forest to the airfield. His driver, Leutnant Erich Kretz, reported seeing Werner von Haeften throw something into the woods in his mirror. This story has now been made into a film called “Valkyrie” Staring Tom Cruise.