Later that evening, "Gipsy" set out with the destroyers , , , and to hunt for U-Boats thought to be minelaying in the North Sea. Just outside the harbour boom she triggered one of the two magnetic mines dropped about 2 hours earlier by two German seaplanes, and, almost broken in half, sank on the edge of the deepwater channel. 31 of her crew, including the captain, Lt-Cdr Crossley, were killed or fatally injured, 115 were rescued by the other destroyers and by harbour launches. The inquiry determined that, though the harbour defences had been on alert (UK National Archive 248 Heavy AA Battery War Diary WO 166/2529), and had actually seen and plotted both the seaplanes and their mines, their reporting had been inaccurate. Though the Harwich admiral had told the destroyers to hug the side of the channel opposite to where the mines fell, he had not stipulated why, nor that the ships were in any particular danger. Apart from those on the bridge, Gipsy's crew were unaware of any danger at all as a result some had gone to sleep below decks, and no contingency plan had been made to ready lifeboats.