It is British and was made by Wallop Industries, How it works,
When the candle rises to a depth of 30 feet, the hydrostatic firing mechanism operates to fire the two detonators as described in Para
t. 4-. The detonators ignite the strip of primed cambric which ignites the gunpowder capsule at the bottom of the smoke unit centre tube. The capsule ignites the delay fuze which takes 10 seconds to burn, allowing the store to settle at the surface, before it ignites the gunpowder capsule at the top of the tube. The top capsule, in turn, ignites the primed cambric, the loose gunpowder and the priming composition in the small chamber. The blast from the loose gunpowder blows out the sealing plug from the nose end of the smoke tube, whilst the priming composition ignites the main smoke composition causing smoke to pass up the tube to atmosphere. The candle will produce smoke and flame for about 5 to 6 minutes.
some more photo's showing the top.


These show the hole for the message tubes and the recess for the fluorescein pack which holds the message tube in place. The four I have also go with these two I got last year,



Roller63 Your one is very nice and seems to be in excellent condition. I haven't seen much in the way of Submarine type pyrotechnics advertised over the years. I handled a drill 65 grenade a couple of years ago but had to give it back as the boat decided its need was bigger than mine.