My Grandad joined the navy at 16, he couldn't swim either and it was at the advice of his 3 older brothers who said if you go into the army you will probably die, 2 of whom never returned from the trenches of WW1.
He served from 1917 through to, I think, 1930 and then went into the reserves so was called up in 1939. He was on board HMS Whitely which was sunk by a dive bomber 19th May 1940 off the coast of Belgium. As his hearing was damaged he wasn't much good on the gun crew anymore - "sorry, did you shout fire?" !!
He then became a storeman on HMS Formidable which also became a target for dive bombers somewhere off the coast of Greece in May 1941. She went for repairs in the USA and then headed for the Indian Ocean, along with his service record I also have his crossing the Equator certificate, issued by King Neptune!
He finished his time based on Hayling Island training the landing craft crews for Sicily, Italy, D-day etc. Due to his age and length of service I'm pretty sure he was de-mobbed by July 45.