This is a rare military watch used on an RAF aircraft camera that was developed for the electric Lightning Interceptor fighter aircraft from the 1960s.
This is an IWC watch marked with a broad arrow and 10AF/807 N.I. 299 on the screw-back.
The inside of the case's back is branded JWC and marked stainless steel.
The movement inside is signed International Watch Co. Also numbered 1811217 between the plates.
CAL 89 movement type.
Seems to be in good working condition. Only issue I can see on mine is the porcelain white dial and the inner black line just above the 6 o'clock number has come off the porcelain, I have seen this sort of paint loss before on other porcelain dials.
There are many websites relating to these interesting camera timer clocks or however they worked. You will see they think there was only about 500 ever made and there will be less complete examples survived as they were taken apart and used for other later timer IWC watches along the way, well here is one which I have had in my collection for about 10 years.
Blued hands and ticking away happy now.
Interesting reading about these and you will see a number for sale on ebay as well as a couple coming through the live auction houses.
Check out RAF Binbrook for more info.