A mishap not unheard of especially during World War 1 was the accidental loss of a submarine due to mines. In the case of the UC-42 on Sept. 10, 1917 the mines were her own. The UC-42 was built at Vulcan in Hamburg and launched on Sept. 21, 1916, less than a year before her loss. The UCII Type boats were coastal submarines mainly used for minelaying operations. At only 161' long and displacing a total of 545 tons they carried only 7 torpedoes and 18 mines.

During a minelaying operation September 10, 1917 off Cork, Ireland the UC-42 and all 27 men on board came to grief when she either struck one of her mines or one of them exploded during deployment. During the war Germany lost several U-boats due to their own mines including the UC-12 the UC-32 and possibly the UC-9.