In German hands "Tyr" was first used together with fellow captured Norwegian minelayer "Uller" in a plan by Admiral Otto von Schrader to mine the entrance to the Sognefjord on 30 April. Together the two ships could carry 80 mines and quite effectively block in the Norwegian naval forces in the country's longest fjord. However, the Norwegian forces in the fjord had a very effective system of look-outs and guard ships. Before the two minelayers even had entered Sognefjord they were attacked by two of the Royal Norwegian Navy Air Service's M.F.11 biplane patrol aircraft. The seaplanes dropped nine bombs at the two minelayers, failing to damage either of the ships but wounding three sailors on "Uller" with shrapnel. Having escaped damage in this attack the minelayers continued north and started laying mines at the entrance to the Sognefjord. In the early hours of 1 May the Norwegians threw another seaplane attack against the German mining operation. A single Norwegian Heinkel He 115 made two dive bombing attacks on "Tyr" and "Uller", dropping one 250 kg bomb and four 50 kg bombs on the fiercely resisting ships. None of the bombs were direct hits, but one near miss damaged the side of "Uller", causing sea water to flood into her. "Uller" had to be beached on Losneøy island and thereafter scuttled by the only slightly damaged "Tyr".