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North Sea Mine Barrage
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North Sea Mine Barrage
The North Sea Mine Barrage, also known as the Northern Barrage, was a large minefield laid easterly from the Orkney Islands to Norway by the United States Navy (assisted by the Royal Navy) during the First World War. 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, described the barrage as the "biggest mine planting stunt in the world's history".
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. A minefield across the North Sea would require mining water 900 feet (270 m) deep, when no minefield had been established in waters more than 300 ft (91 m) deep. A minefield across the North Sea had been estimated to require 400,000 conventional anchored mines. An "antenna" mine developed in July 1917 was effective at the assumed maximum submarine depth of 200 ft (61 m) and 100,000 of these new Mk 6 mines would be adequate to form the North Sea mine barrage.
The United States was altogether more enthusiastic about the operation, as the loss of trans-Atlantic shipping was a major domestic concern and this plan allowed the United States to play an active part in tackling this, while playing to their industrial strength and with minimal risk of American casualties. Franklin D. Roosevelt, the Assistant Secretary of the Navy, appealed directly to President Woodrow Wilson to overcome opposition to the project from Vice Admiral William Sims, who commanded all United States naval forces in Europe. The U.S. Navy tendered an order for the Mk 6 mines in October 1917 with 80,000,000 ft (15,000 mi; 24,000 km) of steel wire rope required to moor the mines to the seabed. Project spending of $40 million was shared among 140 manufacturing contractors and over 400 sub-contractors. All mine components other than wire rope, explosives and detonating circuitry were manufactured by Detroit automobile firms. 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 objective was to prevent U-boats from operating in the North Atlantic and preying on trans-Atlantic shipping. A similar barrage had already been placed across the English Channel, which had resulted in U-boats diverting north around 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 Mk 6 mine was a 34-inch-diameter (86 cm) steel sphere containing a buoyancy chamber and 300 lb (140 kg) of TNT. Each mine was constructed of two steel hemispheres welded together. A Toxyl bursting charge was cast into the lower hemisphere. Toxyl was a mixture of 60% trinitroxylene (TNX) with 40% TNT used because the United States Army controlled United States TNT production and would not release sufficient quantities for the naval mine barrage. For transport, the mine rested atop a box-shaped steel anchor approximately 30 in (760 mm) square. The anchor box had wheels allowing the mine assembly to be moved along a system of rails aboard the minelayer. The mine was connected to its 800 lb (360 kg) anchor box by a wire rope mooring cable stored on a reel. The depth of the mine below the water surface was controlled by allowing the steel mooring cable to unwind from its reel as the mine was dropped from the minelayer until a sensor suspended beneath the anchor reached the bottom. The sensor locked the cable reel so the falling anchor would pull the buoyant mine below the surface; and the float extended the antenna above the mine.
Each mine had two hydrostatic safety features intended to render the mine safe if it detached from its mooring cable and floated to the surface. The first was an open switch in the detonation circuit closed by hydrostatic pressure. The second was a spring pushing the detonator away from the explosive charge into the buoyancy chamber unless compressed by hydrostatic pressure. The mines were intended to be safe at depths less than 25 ft (7.6 m). The mines contained a dry cell battery each with an electrical detonating circuit which could be initiated by any one of five parallel fuzes. Four of the fuzes were conventional horns in the buoyant upper hemisphere of the mine. Each horn contained a glass ampoule of electrolyte which would connect an open circuit if an ampoule was broken 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 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.
The mine barrage was within a belt 230 mi (200 nmi; 370 km) long and 15 mi (13 nmi; 24 km) to 35 mi (30 nmi; 56 km) 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 10 mi (8.7 nmi; 16 km) 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 USS Black Hawk. 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
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North Sea Mine Barrage
The North Sea Mine Barrage, also known as the Northern Barrage, was a large minefield laid easterly from the Orkney Islands to Norway by the United States Navy (assisted by the Royal Navy) during the First World War. 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, described the barrage as the "biggest mine planting stunt in the world's history".
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. A minefield across the North Sea would require mining water 900 feet (270 m) deep, when no minefield had been established in waters more than 300 ft (91 m) deep. A minefield across the North Sea had been estimated to require 400,000 conventional anchored mines. An "antenna" mine developed in July 1917 was effective at the assumed maximum submarine depth of 200 ft (61 m) and 100,000 of these new Mk 6 mines would be adequate to form the North Sea mine barrage.
The United States was altogether more enthusiastic about the operation, as the loss of trans-Atlantic shipping was a major domestic concern and this plan allowed the United States to play an active part in tackling this, while playing to their industrial strength and with minimal risk of American casualties. Franklin D. Roosevelt, the Assistant Secretary of the Navy, appealed directly to President Woodrow Wilson to overcome opposition to the project from Vice Admiral William Sims, who commanded all United States naval forces in Europe. The U.S. Navy tendered an order for the Mk 6 mines in October 1917 with 80,000,000 ft (15,000 mi; 24,000 km) of steel wire rope required to moor the mines to the seabed. Project spending of $40 million was shared among 140 manufacturing contractors and over 400 sub-contractors. All mine components other than wire rope, explosives and detonating circuitry were manufactured by Detroit automobile firms. 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 objective was to prevent U-boats from operating in the North Atlantic and preying on trans-Atlantic shipping. A similar barrage had already been placed across the English Channel, which had resulted in U-boats diverting north around 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 Mk 6 mine was a 34-inch-diameter (86 cm) steel sphere containing a buoyancy chamber and 300 lb (140 kg) of TNT. Each mine was constructed of two steel hemispheres welded together. A Toxyl bursting charge was cast into the lower hemisphere. Toxyl was a mixture of 60% trinitroxylene (TNX) with 40% TNT used because the United States Army controlled United States TNT production and would not release sufficient quantities for the naval mine barrage. For transport, the mine rested atop a box-shaped steel anchor approximately 30 in (760 mm) square. The anchor box had wheels allowing the mine assembly to be moved along a system of rails aboard the minelayer. The mine was connected to its 800 lb (360 kg) anchor box by a wire rope mooring cable stored on a reel. The depth of the mine below the water surface was controlled by allowing the steel mooring cable to unwind from its reel as the mine was dropped from the minelayer until a sensor suspended beneath the anchor reached the bottom. The sensor locked the cable reel so the falling anchor would pull the buoyant mine below the surface; and the float extended the antenna above the mine.
Each mine had two hydrostatic safety features intended to render the mine safe if it detached from its mooring cable and floated to the surface. The first was an open switch in the detonation circuit closed by hydrostatic pressure. The second was a spring pushing the detonator away from the explosive charge into the buoyancy chamber unless compressed by hydrostatic pressure. The mines were intended to be safe at depths less than 25 ft (7.6 m). The mines contained a dry cell battery each with an electrical detonating circuit which could be initiated by any one of five parallel fuzes. Four of the fuzes were conventional horns in the buoyant upper hemisphere of the mine. Each horn contained a glass ampoule of electrolyte which would connect an open circuit if an ampoule was broken 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 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.
The mine barrage was within a belt 230 mi (200 nmi; 370 km) long and 15 mi (13 nmi; 24 km) to 35 mi (30 nmi; 56 km) 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 10 mi (8.7 nmi; 16 km) 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 USS Black Hawk. 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
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