WRECK TOURS OF SUBMARINES are a bit like buses. Just under two years ago, we ran three submarine tours over four months, the last of which was the unusual minelayer U74E (Wreck Tour 142).
Then there was a gap, and this month we tour UC42, from the class of minelaying submarines that U74E was intended to supercede. Unlike buses, we don’t have any more submarine Wreck Tours lined up for a while.
UC-class mine-laying boats are an interesting dead-end variation of U-boat design. Uniquely, they were fitted with vertical mine-tubes.
This feature was rendered unnecessary once mines were developed that could be laid through torpedo-tubes, thus making any submarine capable of laying mines, and removing the operational need for specialist mine-laying classes.
Our UC-class boat, UC42, was sunk in 28m in the approaches to Cork or, from a military point of view, in the approaches to the Royal Navy dock at Queenstown, which has now reverted to its traditional name of Cobh.
Our tour begins amidships, where a large section of cladding is intact above the starboard side of the hull (1).
The UC42 rests on its port side and, somewhat atypically, our route proceeds along the keel to see one of the external bow torpedo tubes (2) lying in the silt beneath the keel.
This would originally have been mounted above the waterline, and forward of the pressure hull.
The wreck must have been rolled at some point, because the remains of the port-bow hydroplane (3) stick out from the keel side of the wreck. The stub of the shaft from the starboard-bow hydroplane (4) is in its rightful location at the top of the wreck, which is the starboard side.
The dockyard divers who inspected the wreck in 1917 reported that the bow was intact, with external torpedo-tubes and reload torpedoes in place.
The domed face between the two is the end of the pressurised hull. I could find no further trace of the bow forward from here.
Above the bow is a small shaft with a bevelled gear (5). This would have been connected to an anchor-winch.
Then, leading aft, there is a line of six mine-laying tubes (6).
Some of these have the rotting remains of mines still inside them, big balls of what looks like foam with bites taken out of it, but is in fact explosive.
Aft of the mine-tubes is a ventilator cover (7), and then an open hatch (8) with its cover removed, perhaps by the Navy divers who visited the wreck to search for code-books soon after its sinking.
Behind the hatch is a conical gun-mount (9), but no sign of the 88m naval gun that would have been mounted on it.The conning tower has been torn off the wreck to leave part of the periscope (10) projecting and a fractured surround (11).
Behind the conning tower, a matching pair of fittings on the hull are air-intakes (12) for the diesel engines.
Next aft from these is the base of the U-boat’s radio mast (13). Immediately behind this is a hole in the hull (14), through which batteries can be seen, and a closed hatch (16) .
The conning tower (15) lies alongside the wreck, with the top pointing forwards, as identified by the upper part of the periscope and the conning-tower hatch.
The divers who inspected the wreck in 1917 reported that the conning tower was intact. I suspect that the damage was caused in 1919, when explosives and wire sweeps were used to reduce the wreck, and further damage may have arisen from the hull being rolled in winter storms.
Continuing aft, just before the hull ends at the stern there is a T-shaped mechanism (17) that would have controlled the aft hydroplanes and rudder.
Inside the stern is a single aft-facing torpedo-tube (18). Then finally, as we round the stern, the highest point of the wreck is the starboard propeller-shaft and propeller (19).
Most of this is covered in big plumose anemones, but the cone of the propeller has been polished by divers’ hands to reveal it as belonging to UC42, and consequently giving positive identification to the wreck.
A little further back on the shaft, the divers who rediscovered the wreck in 2010 have placed a plaque.

Thanks to Hutch Hutchinson and Andrew Ricks.

THE FATAL SIXTH
UC42, mine-laying U-boat. BUILT 1915, SUNK 1917
PART OF THE FLANDERS FLOTILLA, UC42 had completed five patrols since January 1917 before meeting its fate off Cork that autumn on its sixth patrol.
At 3am on 31 October, Royal Navy torpedo-boat TB055 spotted a slick of oil. On the lookout for
U-boats, she followed the slick and dropped a depth charge.
The volume of oil subsequently increased, so the minesweeping trawler Sarba then dropped a further depth charge.
Next morning, minesweeping drifter Sunshine and another torpedo-boat, TB058, reported oil still rising to the surface. On 2 November, divers from the dockyard inspected the wreck and identified it as UC42 from a marking plate on the conning tower.
The only significant damage reported by the divers was to the stern, leading to the theory that UC42 was sunk by one of its own mines.
This seems unlikely, because the explosion of an anti-shipping mine would have caused considerably more damage than simply stripping the stern cladding and control surfaces.
Perhaps the damage to the stern was a result of the depth-charge explosions. Or perhaps it was all an accident.
Submarines launching mines or torpedoes are subject to sudden changes in buoyancy and trim, for which skilled crews have to compensate.
In water as shallow as 28m, Oberleutnant Hans Albrecht Müller, UC42’s commander, would not have much room for error. Uncorrected, the gain in buoyancy at the bow as mines were launched could have caused the stern to strike the seabed.
What we can be sure of is that UC42 was not sunk by TB055’s depth-charge attack on 31 October.
UC42 set out on its last patrol from Flanders on 1 September, and the longest patrol recorded for a UC-class boat was 24 days.
By the end of October, everyone on board UC42 would already have been long dead.
German records give the date of loss as 10 September 1917, the date UC42 was scheduled to return from its sixth patrol.

TOUR GUIDE
GETTING THERE: Unfortunately the Swansea-Cork ferry service has ceased, so the closest ferry route is via Pembroke or Fishguard to Rosslare.
HOW TO FIND IT: The GPS co-ordinates are 51 45.077N, 008 12.909W (degrees, minutes and decimals). The bow points to the north.
TIDES: Slack water coincides with high and low water Cobh, but is only really necessary on spring tides.
diving & air Liveaboard and RIB diving with Ocean Addicts, www.oceanaddicts.ie
DIVING & AIR: Liveaboard and RIB diving with Ocean Addicts, www.oceanaddicts.ie
ACCOMMODATION: Ocean Addicts operates the fleet tender liveaboard Embarr, with on-board accommodation for 12 divers.
LAUNCHING Numerous slips are available in the estuaries at Kinsale and Cork..
QUALIFICATIONS: PADI Advanced Open Water Diver or BSAC Sports Diver
FURTHER INFORMATION: Admiralty Chart 1765, Old Head Of Kinsale To Power Head. Cork diver Tony O’Mahony runs the website www.corkshipwrecks.net, with a wealth of background information on UC42 and many other wrecks.
PROS Easy to navigate in typically good visibility.
PROS: A perfectly sized wreck for a no-stop dive with the appropriate nitrox mix.
CONS: Harder to get to now that the Swansea-Cork ferry service no longer operates.

DEPTH
-20m width=100%
20m-35mwidth=100%
35m-45mwidth=100%
45m+width=100%
DIFFICULTY RATING
width=100%width=100%width=100%width=100%width=100%