Northern Barrage

The objective of a defensive minefield is to restrict movement of enemy ships into areas used by friendly shipping. The assumed presence of a minefield may have a morale effect of assumed risk in addition to actually damaging ships attempting to cross the field. In July 1939, before World War II had begun, the possibility of a Northern Barrage between the Orkney Islands and Norway (similar to the North Sea Mine Barrage of World War I) had been considered. Other alternatives were investigated after the occupation of Norway by the Germans in April 1940. American Mk 6 mines had been used for the deeper water portions of the World War I mine barrage. The Royal Navy standard Mk XVII mine inventory available for use at the outbreak of World War II lacked an antenna fuze. The Mk XVII mine could be suspended at depths as great as below the surface anchored in water as deep as . Those depth capabilities suggested the possibility of laying mines along the Iceland–Faeroes Ridge, a submerged mountain range between Iceland and the Faeroe Islands which separates the deeper portions of the Norwegian Sea to the north and the Atlantic Ocean to the south. The ridge top is less than below the surface and significantly shallower east of Iceland and on the Faeroe shelf. Channels are deep between the Faeroe shelf and Scotland and in the Denmark Strait between Greenland and Iceland. Mk XVII mines would be laid in the shallower areas while the antenna-fuzed Mk XX mine was under development. Gaps were planned to allow passage of the fleet and convoys. ==Navigation==

Maintaining precise records of minefield locations is an important element of defensive minefields, since these minefields are often close to waters traditionally used by friendly shipping. Most defensive minefields had historically been within visual distance of navigational aids establishing precise locations. Laying the Northern Barrage in waters so far from land was a challenging navigational problem before Global Positioning System information was available. Much of the preparatory survey work was completed by the survey vessel . Scott later operated with the minelayers placing the deep water minefields from the spring of 1942 until minelaying was discontinued in the autumn of 1943. Scott helped establish the boundaries of adjacent minefields so the minelayers could minimize un-mined gaps without accidentally straying into previously mined areas. ==Laying the barrage==

The first Minelaying Squadron, based at Kyle of Lochalsh (code-named port ZA for secrecy), was formed in June 1940. Five fast and modern cargo liners were requisitioned from civilian service, but the conversion to auxiliary minelayers , , , and was not completed until October. Arrival of Town-class destroyers from the Destroyers for Bases Agreement provided necessary escorts for the minelayers. The first minelaying mission left port ZA on 18 October 1940, and 10,300 conventional contact mines were laid at the southern end of the Iceland–Faeroes Ridge before the end of the year. Every ship struck mines. There were no crewmen lost aboard the Soviet freighter Rodina (4441 GRT), the Panamanian-flagged freighter Exterminator (6115 GRT), or the American freighter Hybert (6120 GRT); but 46 civilian crew and 9 Naval Armed Guards died aboard the American Liberty ship John Randolph (7191 GRT) and freighters Hefron (7611 GRT) and Massmar (5825 GRT); and there were only eight survivors of the 127 men aboard Niger. Only Exterminator could be salvaged. The value of the Northern Barrage was questioned following the accident, though new fields were laid south of Iceland, before starting new deep fields on the Faeroes shelf. ==Cancelled==

remains visible where the minelayer exploded preparing to leave the first Minelaying Squadron's base at Port ZA. The future of the Northern Barrage was discussed by the Admiralty at meetings in January and July 1943. Escorts allocated to protecting the minelayers had created a shortage of convoy escorts. The barrage had proved difficult to maintain in March 1942, in July 1943 and in September 1944. The Allies were unaware of these U-boat losses and attributed most of them to Allied ship and aircraft attacks after the Commander-in-Chief of the Home Fleet declared the Northern Barrage "the least profitable voluntary major undertaking of the war". The programme was cancelled and apart from the laying of an additional field at the entrance to the Denmark Strait, the only minelaying approved was a series of deep fields at the northern end of the Faeroes–Iceland gap. The First Minelaying Squadron was disbanded after laying 92,083 mines. The minefield represented 35 percent of all British minelaying effort during the war. The Northern Barrage had failed to justify its existence and had often been more dangerous to Allied forces than to the Germans. Afterwards more effort was deployed on offensive minelaying by submarines, motor launches and aircraft, which proved far more effective. ==Legacy==

Not all of the mines were removed or destroyed during or following the war and unexploded mines have been discovered into the twenty-first century. Most of the steel shell has corroded unless protected by burial in anaerobic sediment; but the cast explosive charge may still be intact. The most commonly used mines included or of explosives. TNT was the most commonly used explosive, although it was sometimes mixed with ammonium nitrate (forming Amatol) for economy and with powdered aluminum (forming Minol) to increase underwater damage. ==References==