I am watching 'THE CRUEL SEA' as I type and the number painted on the side of the U boat is U53 not U153. Now this does not mean anyone is wrong it may be this was added in post production and different prints exist. Over to anyone who can help solve this puzzle. I am an ex submariner having served in the RN spending my final 61/2 years on Super 'O' boats. Onslaught and Ocelot. The latter is currently on display at the former naval dockyard at Chatham.