HMS/M Grampus (SO4) sits upright in 120m, making it beyond the range of most recreational divers. Built by Cammell Laird at Birkenhead, she is one of eight porpoise class submarines. She was commissioned in 1958. She sank on the 18th September 1980 whilst being towed to be used as a sonar target in upper Loch Fyne.
She is 88m long with a beam of 8m, she used to carry a complement of 71 officers and men.