In the late afternoon of Wednesday the 14th July 1909, HMS Bonaventure and 8 submarines of the 6th flotilla left Grimsby along with 8 torpedo boats. At 23.45 of that night with foggy conditions, the flotilla and torpedo boats were travelling at 11 knots and were 4.5 miles from the Happisburgh Light. The C11 was leading the formation. Heading in the opposite direction was the collier SS Eddystone. The Eddystone had not been informed of the flotillas presence in the area. With the Eddystone attempting to cross the line of the Flotilla, submarines and torpedo boats swung to avoid collision with the steamer. The C11 was struck by the Eddystone whose bows tore into the stern of the C11 sending the submarine straight to the bottom. The wreck of the C11 was discovered in the 1990s.

During salvage operations the C11 was raised 50 feet off the seabed. Whilst being towed beneath two lighters the C11 struck an underwater object and became held fast. HMS Vindictive remained on site for a further 6 weeks in order to assist in the salving of C11 with no success. At the time of salvage operations the C11s periscope was recovered along with fittings from the conning tower.

Before leaving the site of the ill fated C11 a funeral service was given on board HMS Vindictive in honor of the lost crew.  

The C11 is well sanded in, she still retains her cigar shaped like hull, her prop and rudder are still in situe. Salvage attempts were made in order to raise the C11, but were abandoned in September 1909. One body was recovered, however the remains of the other twelve lost crew members still remain within the pressure hull of the C11. Please treat this site with the respect it deserves with this in mind.