company of her sister minelayer, USS Shawmut. This voyage, aided by the novel technique of refueling at sea, took her to Scotland, where in July she participated in laying the North Sea Mine Barrage, laying thousands of mines across the mouth of the North Sea in order to create a barrier for German U-boats trying to depart from German seaports to the open Atlantic. Aroostook laid a total of 3,180 mines in this operation: planted 320 mines during the 3rd minelaying excursion on 14 July, planted 320 mines during the 4th minelaying excursion on 29 July, planted 290 mines during the 5th minelaying excursion on 8 August, planted 330 mines during the 6th minelaying excursion on 18 August, planted 310 mines during the 7th minelaying excursion on 26 August, planted 290 mines on 30 August to complete the 7th minefield after was unable to lay its mines, planted 320 mines during the 9th minelaying excursion on 20 September, planted 330 mines during the 10th minelaying excursion on 27 September, planted 330 mines during the 11th minelaying excursion on 4 October, and planted 340 mines during the final 13th minelaying excursion on 24 October. This effort, nearly completed, was the major operation of the U.S. Navy in European waters during World War I, and it came to an end on 11 November 1918 with the Armistice with Germany and the end of fighting in World War I. USS Aroostook steamed home to the East Coast in December 1918 An aircraft tender, 1919–1931 During the spring of 1919, USS Aroostook was refitted as an "aircraft tender" to support the attempt by U.S. Navy naval aviators to make the first transatlantic crossing of the Atlantic Ocean by air. The Navy had four huge Curtiss NC floatplanes built for the project. These aircraft were twice the size of contemporary aircraft. The route for this attempt used southeastern Newfoundland and the Portuguese Azores Islands as stopping-off points for refueling and maintenance work on the new planes, and for rest and mess periods for their aviators. In the event of the attempt, mechanical problems and lack of replacement parts necessitated the cannibalization of one of the aircraft, leaving three "Nancys" for the attempt. During the first half of May 1919, Aroostook was waiting at the port of Trepassey, Newfoundland, to serve as a floating base for the three medium-sized Curtiss NC floatplanes that took off from