National Museums Liverpool Blog - The mine offensive

The oil tanker El Oso. Image courtesy of the Liverpool Daily Post & Echo.

Some years ago a common sight at seaside resorts and elsewhere was old deactivated German sea mines that had been converted into charity collecting boxes. These round menacing floating mines had one or more slots cut in them and your penny clattered around inside after you shoved it in. German mines exacted a terrible toll in the early months of the Second World War when almost 400 British, allied and neutral ships were sunk and many more damaged.

Thousands of mines were laid around British coasts by U-boat submarines, destroyers, mine layers and aircraft. By early 1940, German mines and aircraft had also effectively closed the Port of London to ocean-going ships. This led to the diversion of most of the capital’s usual traffic to the comparatively safer west coast ports of Liverpool, Glasgow and the Bristol Channel.

Liverpool, the largest and most central of these ports, was Britain’s most important port throughout the rest of the war.At this period German aircraft and U-boats were also laying mines around many of Britain’s west coast ports, including Liverpool. Many ships were sunk or damaged in Liverpool Bay, causing large disruption to the port’s activities.

British boffins hit back at the mine threat by fitting the hulls of most large British ships with degaussing cable to neutralise the ship’s magnetism. This greatly reduced the threat from magnetic mines. On display at Merseyside Maritime Museum is a huge, seven-foot long German sea mine which almost breathes menace. It was designed as a magnetic mine for use against ships. These were dropped by aircraft using a parachute or by ships – it was one of Germany’s most secret weapons at the start of the war. The mines carried 1,536 lbs of high explosives. They were also dropped as bombs on Liverpool, London and other British cities, causing devastation.

An illustration from a wartime book shows how a magnetic mine works. The mine lies on the seabed waiting for a ship to pass. Impulses from the metal hull of the ship detonate the mine, causing a huge explosion. The oil tanker El Oso is seen sinking after passing over such a mine, laid by the U-30, in January 1940. She was the first to be sunk by German mines in Liverpool Bay during the war.

Merseyside Maritime Museum is open seven days a week, admission free. A new Maritime Tale by Stephen Guy appears every Saturday in the Liverpool Echo. A paperback – Mersey Maritime Tales (£3.99) – is available from the museum, newsagents, bookshops or from the Mersey Shop website (£1.50 p&p UK).