In 1941, HMS Perseus struck a mine and sank off a Greek island. John Capes was the only survivor.
Sources:
1. HMS Perseus (Wikipedia) — Good overview of the entire story, including the sinking, Capes' escape, his 5-mile swim, the 18 months on Cephalonia, and the 1997 wreck discovery.
2. Royal Navy Museums – Submarine Museum — Official Royal Navy museum. While it's the museum homepage rather than a page devoted solely to Perseus, it's an excellent authoritative source for submarine operations and escape equipment.
3. Royal Naval Association – Semaphore Circular (December 2024 PDF) — Surprisingly good. This PDF has a concise summary of the Perseus story, including:
mine strike
61 men aboard
John Capes hitching a ride
Davis escape apparatus
50 m (≈170 ft) ascent
5-mile swim
18 months hidden
wreck found in 1997
4. UK National Archives — Not about Capes specifically, but the official guide to Royal Navy ship-loss records if you ever want to verify details from original wartime documents.