TRENCHANT and the Turtles – the Fleet Submarine TRENCHANT, on station in the Indian Ocean, visited of Diego Garcia (a British Overseas Territory) for a six day break, being the first British submariners to call in at the US Naval and Air Base in five years.    Members of the crew helped marine life experts research the giant turtles on the atoll by tagging rare marine life, and celebrating the traditional naval ceremony of Crossing the Line.