Also known as: UC-42, UC42, U-boat UC-42
The crew of UC-42 were laying mines to destroy other ships when one of their own mines destroyed them. On 10 September 1917, this German UC II-class minelaying submarine was deploying a minefield at the entrance to Cork Harbour off Roches Point when a mine detonated, killing all 27 crew instantly. The wreck was relocated by divers in 2010 in approximately 28-30 metres and subsequently designated a war grave under the National Monuments Acts. She rests on her port side with the keel visible and an external bow torpedo tube lying in the silt beneath. In 2024, divers from Blackwater Sub Aqua Club and Mizen Archaeology recovered one of the propellers after months of careful excavation -- a significant maritime heritage event covered by RTE and the Irish Examiner. A licence under the National Monuments Acts is required to dive this protected site.
On 10 September 1917, UC-42 was laying mines at the entrance to Cork Harbour when one of her own mines detonated, destroying the submarine and killing all 27 crew instantly. The boat was on a mission to mine the approaches to one of Ireland's busiest ports. The cause was likely a malfunction during the mine-laying process — a known hazard for UC-class boats, several of which were lost to their own mines during the war.
SM UC-42 is a submarine wreck located off Cork, Ireland at a depth of 30 metres. The vessel was lost due to mine (own) in 1917. The wreck is diveable.
SM UC-42 lies at 25 to 30 metres depth, Approximately 5 nautical miles south of Roches Point, Cork Harbour.
SM UC-42 was destroyed by one of her own mines on 10 September 1917 during World War I, off Cork, Ireland. 27 people lost their lives.
Diving the SM UC-42 is rated advanced and is requires an Advanced Open Water certification with wreck diving experience. Minimum certification: Advanced Open Water. Recommended: Deep diver specialty.
The best months to dive SM UC-42 are April, May, June, July, August, September. Water temperature ranges from 8.5°C in winter to 15°C in summer.
SM UC-42 is accessed by boat from Cobh, Cork, Ireland. The wreck is a designated war grave.
| Month | Temp | Visibility | Access | Marine life |
|---|---|---|---|---|
| Jan | 9.0°C | 5.0m | fair | approximate |
| Feb | 8.5°C | 5.0m | fair | approximate |
| Mar | 9.0°C | 6.0m | fair | increasing |
| Apr | 9.5°C | 7.0m | good | moderate |
| May | 10.5°C | 8.0m | good | good |
| Jun | 12.0°C | 10.0m | good | good |
| Jul | 14.0°C | 10.0m | good | excellent |
| Aug | 15.0°C | 10.0m | good | excellent |
| Sep | 14.0°C | 8.0m | good | good |
| Oct | 12.5°C | 6.0m | fair | moderate |
| Nov | 11.0°C | 5.0m | fair | moderate |
| Dec | 10.0°C | 5.0m | fair | approximate |
6 evidence records from 6 sources.
Approximately 5 nm south of Roches Point, Cork Harbour
The UC42 rests on its port side, with the route proceeding along the keel to see one of the external bow torpedo tubes lying in the silt beneath the keel.
Own mine detonated while laying minefield off Roche's Point, 10 September 1917. All 27 crew lost.
UC-42 sank on 10 September 1917 when a mine she was carrying exploded, killing all 27 crew.
Blackwater Sub Aqua Club and Mizen Archaeology carried out a recovery operation of the submarine's propeller, raising it from 30m depth.
Approximately 5 nautical miles south of Roches Point, Cork Harbour