Mines

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When Britain went to War in August 1914 it was very much the Admiralty's policy that Mines were primarily the weapon of the weaker naval power. As a consequence the British possessed a stock of only some 4,000 mines. These being of a primitive design, being activated by a horizontal firing arm that released a spring loaded firing pin against percussion detonator when stuck by a ship. The only means of mine laying were seven old cruisers converted to carry 100 mines each. However the technique of minesweeping had been extensively studied and a number of gunboats had been converted to mine sweepers, with Naval Reserve personnel trained in their use.

In contrast the Germans had a large stock of efficient buoyant contact mines activated by the Herz horn firing gear. This system utilised a number of lead covered horns each encasing a glass tube containing a Bichromate solution. When the horn was bent by contacting a passing ship, the glass tube broke releasing the liquid to come in contact with a zinc and carbon plate, thus creating an electrical battery. The electric current then flowed through a fuse wire to explode a mercury detonator.

The Mine war started on the night of the 4/5th August 1914 when the minelayer Konigin Louise aid a minefield about 40 miles off Lowestoft. She was intercepted and sunk by the light-cruiser Amphion, which in turn struck one of the recently laid mines and sank too.

 

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Initially British mine-laying activity was confined to countering the threat from German U-boats in the Straits of Dover and blockading their base at Brugges. However, on the 27th of October the new dreadnaught Audacious was lost off of Tory Island, northwest of Ireland. This would lead to a decision by the Naval Commander in Chief to commence the laying of Mines in the Heligoland Bight.

Both sides stepped up their mine laying during 1915. The British converting several passenger steamers to minelayers whilst the Germans modified some U-boats for the same purpose. Throughout 1915 and 1916 both belligerents kept up their efforts. The Germans enjoying a slight advantage because of their earlier start in both quality and quantity. In 1916 the cruiser HMS Hampshire went down after hitting a mine (thought to have been laid by the submarine U-75), resulting in the death of the War Minister Lord Kitchener who was travelling in her to Russia.

 

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From 1917 the mining war turned dramatically in the allies favour. Improved mine clearance techniques would make the mine less of a threat to allied shipping, whilst at the same time the introduction of the Mk H11 with Herz system horns would give the foe a taste of their own medicine. A proposal by Admiral Sir David Beatty in January 1917 for the laying of 60,000 mines however could not be implemented because there simply was not sufficient mines available at that time to make the plan feasible. Nevertheless extra mines were laid in such quantities within the German sea-lanes that were to take a considerable toll amongst German shipping. The Germans only being able to keep a few main sea routes open.

By the end of WW1 the British had laid 128,000 mines which destroyed 150 enemy warships and auxiliaries including some 35 U-boats. In return 43,000 German mines sank 40 British warships and 225 Auxiliaries plus about a million tons of allied merchant shipping.