After training Jack was posted to HMS Jamaica and spent 18 months or so on convoy escort duties, variously on Atlantic and Arctic routes. It was bitterly cold, and they suffered damage and casualties in action; one fellow deck officer was killed by an exploding shell only about ten yards from Jack. It was not nice, but the convoys were bringing vital supplies, and convoy escort was essential. They were also involved in keeping the German heavy ships bottled up in the Baltic.

When Jack joined the navy he found that most of the people in charge were very young and sometimes not very knowledgeable. It was better to listen to Petty officers who had experience. He also wanted to work in smaller ships rather than the Light Cruiser sort of thing, and after about 18 months transferred to Motor Torpedo Boats. From the start of 1944 it had been clear that there would be an invasion and they were on constant patrol amid very tight security; there was a period when they were encouraged to leak misinformation, and that was quite successful.