All those who claim that submarines carrying Trident missiles are vulnerable to “emerging technologies” such as underwater drones (Letters, 17 July) should spend some time at sea. They would then realise the world’s oceans are vast, deep, impenetrable to sound and radio waves, and terminally hostile to the sort of small, battery powered, autonomous drone they envisage. Submarines are just as difficult to detect now as they were in the second world war. I don’t see that changing during the lifetime of the projected replacements to the Vanguard-class submarines.

Nick Batho

Captain RN (rtd), Withypool, Somerset

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