by bending the soft metal horn. The novel fifth fuze was a copper wire antenna with a float to extend it above the mine. A ship's steel hull touching the copper antenna would form a battery, and seawater acted as an electrolyte completing a circuit with an insulated copper plate on the mine surface to actuate a detonating relay within the mine. The relay armature was initially set to complete the detonating circuit at 25 to 40 millivolts. The Bureau of Ordnance subsequently increased sensitivity to 10 to 25 millivolts, but this was later readjusted on the basis of field experience. Each mine had five separate spring-loaded safety switches in the detonating circuit held open by salt pellets which took about 20 minutes to dissolve in sea water after the mine was dropped overboard from the minelayer. Battery life for the detonating circuit was estimated at greater than two years. Laying the minefield The mine barrage was within a belt long and to wide divided into area B off the east coast of Orkney, area C near the Norwegian coast between Utsira and Bergen, and the longest central area A connecting the two coastal areas between 0° 50′ West and 3° 10′ East. The Royal Navy laid mines in areas B and C while the United States Navy mined area A. The Royal Navy left a channel open for navigation adjacent to Orkney. Because of neutrality regulations no mines were laid within Norwegian territorial waters. The United States North Sea Mine Force was commanded by Rear Admiral Joseph Strauss aboard the Atlantic Fleet Mine Force flagship . Strauss was an ordnance specialist and had been chief of the Bureau of Ordnance from 1913 to 1916. Mine Squadron One, under the command of Captain Reginald R. Belknap, assembled at Inverness, Scotland in June 1918. Over the following five months, these ships planted 56,571 of the 70,177 mines laid to form the North Sea mine barrage. The WWI Mine Memorial on Boston Common, Massachusetts, United States (old protected cruiser converted in 1911 to carry 170 mines) (flagship) (old protected cruiser converted in 1915 carry 180 mines) (former Eastern steamship Bunker Hill carried 320 mines on one deck) USS Shawmut (former Eastern steamship Massachusetts carried 320 mines on one deck) (former Southern Pacific freighter El Siglo carried 830 mines on 3 decks) (former Southern Pacific freighter El Dia carried 830 mines on 3