County Cork

Ireland

SM UC-42 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy during World War I. The U-boat was ordered on 20 November 1915 and was launched on 21 September 1916. She was commissioned into the German Imperial Navy on 18 November 1916 as SM UC-42.

UC-42 sailed on her last patrol on 1 September 1917.
On 31 October 1917 Torpedo Boat TB 055 was accompanying minesweepers operating at the entrance to Cork harbour. At 1500 hours an oil track was seen floating on the surface of the water. Following it to its source, TB 055 used its hydrophone to see if the oil was coming from a submarine. Loud mechanical sounds, of "hammering" and "turbine-like noises" were reported and, believing this to be a U-boat, a marker buoy was dropped, followed shortly after by a depth charge. Following detonation of the charge, TB 055 returned to the area and found that the volume of floating oil had increased, and there were bubbles rising to the surface.

TB 055 signalled the nearby armed minesweeper HMT Sarba for assistance. Sarba used her hydrophone but detected no sounds from the presumed submarine. A second depth charge was dropped and Sarba remained on station overnight. The following morning HMD Sunshine and TB 058 swept around the spot, to confirm that the incident had not been a false alarm caused by old wreckage. On 2 November oil was still coming to the surface and dockyard drivers arrived to inspect the assumed wreck. The divers reported a German U-boat lying on the seabed with her stern blown off, and a brass plate on her conning tower reading "C42, 1916" identified her as UC-42. No survivors were ever reported even though some of the hatches were found to have been opened. It was thought likely that the submarine had been sunk by one of her own mines detonating under her stern while minelaying.
When the sinking and identification of the submarine was reported, the British Admiralty requested an identifiable item from the vessel for verification purposes, and in December 1917 divers recovered the telephone buoy from the conning tower. The Royal Navy's Naval Intelligence Department were aware of submarine's 1 September departure date from Belgium and were sceptical about the hammering and engine noises reported by TB 055. The Admiralty reported that "The longest known cruise of a UC boat in home waters is 24 days, so UC42 must have been dead long before TB 055 and Sarba dropped the depth charges"

The wreck was relocated on 6 November 2010 in 27 metres (89 ft) of water, just off Roche's Point, by a group of Irish, amateur divers. It was found with "little obvious explosive damage". A serial number stamped on its propeller allowed positive identification of the wreck.

A plaque was placed by the boats stern and under International Maritime Law she is now a War Grave, untouchable and the responsibility of the Deutsche Marine. Source: wikipedia.org

Out of Cork Harbour via Cork or Crosshaven.