The Royal Navy’s submarine fleet is entirely nuclear powered. In the 80s, though, this was not the case. The Navy then still had a substantial fleet of diesel subs. The Oberon Class of subs was available in numbers along with the remaining Porpoise Class that preceded them and these were due to be replaced by the Upholders. Only four of those were built and they were sold to Canada when the decision was made to get rid of the diesel fleet despite their outstanding stealth qualities. When I went to Navy Days in Portsmouth in the 80s, you could see the subs on display. HMS Dolphin was just across the harbor and was the headquarters of the sub operations. One visit included the chance to see a sub in dry dock – something I suspect would not be left on view these days.