The North Sea Mine Barrage

U.S. Minelayers in Planting Formation

On 8 June 1918, the U.S. Navy began laying mines in the North Sea Mine Barrage. By war's end, the U.S. Navy had placed a total of 56,570 sea mines, helping to create a 300-mile barrier against Germany, stretching from Scotland to Norway. At least five U-boats were sunk by the barrage and many others forced to waste valuable time avoiding the mines.

The mine laying effort was a huge project from creating a technology from scratch and implementing it in a few months. Admiral W. S. Sims described it in an address to the Minelaying Squadron in Portland England, December 1918: 

After we came into the war we designed a mine, built it, equipped the mine layers, sent them over, and planted more mines in less space of time than any nation in the world ever thought of doing–one of the finest stunts the Navy has accomplished on this side.

Location of the Barrage

From a seemingly innocent material called wire rope came the ability to lay and anchor the sea mines in an effective manner. The wire rope had to be developed beyond the civilian sizes and quality and be produced in quantity way above that already needed for other parts of the United States industries. Over two hundred million feet of wire rope was eventually required for the North Sea Mine Barrage. No wire rope failed in action.

Twenty-six operations were required to produce the specific types of wire rope needed. From steel ingots to pulling steel rods through dies, to bathing, baking, and cooling each redrawing, then the actual rope making began. The steel wire was squeezed and twisted and spooled. The sea mines were the other aspect of this technology, and although mines had been around for decades, a new device had to be created to withstand the rigors of the environment and with the power to carry out their mission. The deployment of individual mines is shown in the diagram at the end of the article.

Mark VI Mine and Base

U.S. Rear Admiral Joseph Strauss, commander of the American mining operations in the North Sea, wrote in June 1918: "The mines carried 300 lbs. of T.N.T. and the explosion of such a mine would be quite effective at the several depths. It was decided to plant an upper row of mines at a depth of 45 feet, the middle row at a depth of 160 feet and the lower row at 240 feet." 

When the decision was made to proceed with the North Sea Mine barrage, only two modern minelayers were active in the U.S. Navy. With over 5000 mines to lay a week, advances in laying techniques and actual mine layers had to be advanced rapidly. Obsolete minelayers were quickly updated and other suitable vessels were converted.

The effort after the war to recover the mines was no less important and as staggering in proportions and time restraints as the creation of the mine barrage. The U.S. volunteered to remove all mines laid by the U.S. Navy with sweeping operations started less than four months after the Armistice.

Sequence After the Mine Is Released

The great success of the mine barrage as both a weapon and a deterrent was unqualified. The secretary of the Navy, Josephus Daniels, related that "the mine as a weapon of nautical warfare now presents greater possibilities than ever before." 

Source: Paper by Doran Cart of the Liberty Memorial at the 2009 Western Front Association—Great War Society National Seminar