Nomenclature and history of original Swith No.10?

**WWIIBuff** · 6th January 2022, 12:10 AM

Hello Gentlemen,

What is the formal name of the early (original?) version of the Switch No.10, and can you refer me to a source somewhere to learn about it's development and use?

Is it just called the Switch No.10, whereas the later models that were so widely used are called the Switch No.10 Mk.I, and the post 1943 Mk.II?

Also, were the rings that were painted on these also done in different colors to represent the various delay periods, or was it the number of rings painted that provided that information?

Thanks for your help.

John

**sgtlynn** · 7th January 2022, 04:33 PM

Some information in here http://tgrm.foxed.ca/boobytraps/tbrm%201.pdf

**sgtlynn** · 7th January 2022, 04:49 PM

Initially nicknamed "Signal Relay"
, it was also given the designation SR1.

**WWIIBuff** · 7th January 2022, 05:46 PM

Thanks sgtlynn. I completely forgot about The Booby Trap Manual reference. It has all the information I was looking for on this.

By the way, that is a great avatar image you have!

**Houndsworth** · 21st January 2022, 01:11 AM

Switch No. 10 was the name after it was improved with another inspection hole, the tube containing striker, spring, fuse snout was aluminum (later American ones were brass there), and another inspection hole was added. The safety was a metal strip color coded with the delay time.

I think the original Signal Relay term was a code name to conceal the type of device it was. Delay switch is a good description because they "switched-on" meaning initiated an explosive percussion cap that in turn fired the fuse, detonator, or explosive cord. Some call these "pencil detonators" but detonating is not exactly what they did on their own.

**Houndsworth** · 2nd July 2022, 09:25 PM

I just spotted this conversation. The "Signal Relay" term was indeed a code name invented by the explosives and incendiaries development Section D of the Secret Intelligence Service when it was moved from Bletchley Park in late 1939 to get it away from the code breaking going on there. It went to Aston House at Stevenage in Hertfordshire. This operation was given the cover name Signals Development Branch Depot No. 4, War Office. So their first important device had "Signal" in its name. In 1941 Aston House became War Department Experimental Station 6 or ES6 WD. The 6 is a legacy number that came from MI6 which is the organization who started these secret, "dirty tricks" operations. In 1941 these operations were organized and called Special Operations Executive, a secret name. Aston House was also known as Station XII. There - more than you wanted to know.