Details of the damage inflicted on UC-55 had been recorded by the crews of the British warships, which had struck first the conning-tower and then the hull. The team enjoyed a bottom-time of around 35 minutes on the wreck and succeeded in putting its identity beyond doubt. Torpedo-tube cap (Martin Mako Janeček) Mine ready to launch (Martin Mako Janeček) UC-55’s hull (Martin Mako Janeček) Their efforts on the day were backed up by the Valhalla crew of Helen Hadley and Brandon Rowlands, with the support of wreck-researchers Kevin Heath and Wayne Allen.

The divers were Jacob Mackenzie, Toni Norton, John & Tracy Timperley, Craig Stevenson, Thomas Zloch and Martin Mako Janećek, all diving on closed-circuit rebreathers except for Tracy Timperley, who was back-up diver and on open-circuit. Valhalla’s owner and captain Hazel Weaver says that the technical dive-team had spent a decade planning their dive to check out the wreck. The wreck-site had been picked up on a side-scan sonar survey in 1985, lying upright to 5.6m off the seabed, but because of its depth it would have proved challenging to dive at the time. It sank with the loss of 10 lives, including its commander Oberleutnant zur See Horst Ruhle von Lilienstern, and 17 men were taken prisoner. Two Royal Navy destroyers, HMS Tirade and HMS Sylvia, and the armed trawler Moravia shelled and finally depth-charged the German sub. The forward compartment flooded as a result, forcing the U-boat to surface but leaving it unable to manoeuvre because the batteries had failed. Detonators on UC-55 (Martin Mako Janeček) Antenna connection to the conning tower (Martin Mako Janeček) One of the propellers (Martin Mako Janeček)

The submarine had been about to start laying mines about eight miles south-east of Lerwick, in the convoy channel between Orkney and Shetland, when a trim problem led it to dive beyond its 50m operating depth. Over six patrols, UC-55 had already been credited with sinking nine merchant ships and damaging two more, as well as the destroyer HMS Albacore, in the months before it met its end off Shetland on 29 September, 1917. Fifty metres long, it carried 27 crew and was fitted with six 39in mine-tubes with 18 mines one stern and two bow 20in torpedo-tubes with seven torpedoes and a 3.5in deck-gun. The 415-tonne UC-11-class submarine was commissioned into the German Imperial Navy in November 1916. Rebreather divers from the Orkney-based diving liveaboard mv Valhalla became the first to visit the German mine-layer SM UC-55 on 21 July – at a maximum depth of 104m.

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