The objective was to inhibit the movement of U-boats from bases in Germany to the Atlantic shipping lanes bringing supplies to the British Isles.

Rear Admiral Lewis Clinton-Baker, commanding the Royal Navy minelaying force at the time, described the barrage as the "biggest mine planting stunt in the world's history.

[2] The idea of a mine barrage across the North Sea was first proposed in the summer of 1916 by Admiral Reginald Bacon and was agreed at the Allied Naval Conference on 5 September 1917.

The Royal Navy—and in particular Admiral Beatty as Commander in Chief of the Grand Fleet—was skeptical about the value of the operation and did not feel it justified the large logistical and manufacturing commitment required.

Assistant Secretary of the Navy Franklin D. Roosevelt appealed directly to President Woodrow Wilson[4] to overcome opposition to the project from Vice Admiral William Sims, who commanded all United States naval forces in Europe.

[6] Eight civilian steamships were converted to minelayers; and another 24 mine-carrying freighters, sailing at a rate of two or three per week, were required to transport manufactured mine components to assembly depots in Scotland.

The North Sea Mine Barrage was intended to close this alternative route, and it also made it hard for the U-boats to get supplies.

The Royal Navy left a 10 mi (8.7 nmi; 16 km) channel open for navigation adjacent to Orkney.

Where possible, longitude was determined from a calibrated taut-wire anchored near a landmark and unreeled from a 140-mile (230 km) spool of piano wire aboard one of the cruisers acting as the minelaying formation guide.

A covering force of battleships with Royal Navy cruiser squadrons maneuvered nearby to defend the minelaying formation, but no German surface warships attempted engagement.

About one percent of the mines deployed during the first excursion broke free of their mooring cables and washed ashore in Norway within a month.

Premature detonations increased to 14 percent for the fourth minelaying excursion because some mines had been assembled with the more sensitive antenna fuze relay settings made by the Bureau of Ordnance.

San Francisco identified relay armature sensitivity as a major cause of premature detonations during a comparative field test minelaying excursion on 12 August.

Subsequent investigations revealed copper sulfate deposits caused by antenna corrosion created a weak battery, increasing the probability of relay activation by shock wave accelerations when nearby mines detonated.

[1] United States participation in the minesweeping effort was overseen by Rear Admiral Strauss aboard the repair ship Black Hawk, from which he had commanded the minelaying operation.

While held underwater by planing devices called "kites", the wire would foul the cables suspending the buoyant mines above their anchors.

The winter was spent testing an electrical protective device to reduce the risk of sweeping the antenna mines with steel-hulled ships.

Twenty Admiralty trawlers with American crews, 16 more Lapwing class minesweepers, and another repair ship Panther were assigned to his command.

Two men were killed in separate incidents while attempting to haul mines aboard to clear fouled sweeping kites.

Some of this countermining was attributed to acceleration of the antenna fuze relay armature or seawater leaking into damaged mines rather than sympathetic detonation of explosives.

Three more men of the minesweeping force were killed in individual accidents involving sweeping gear before Strauss declared the barrage cleared on 30 September 1919.

[21] The minesweepers found only about 25 to 30 percent of the mines laid a year earlier;[22] but it was assumed the others had either broken free, sunk to the bottom, or been destroyed by premature explosions.