A large but often overlooked object on Hythe Quay tells a story of shipwrecked sailors, our island's desperate fight for survival, and a deadly weapon that still threatens sudden death to mariners.

The brightly painted sea mine near the Queen's Head is of one of 60 used at coastal locations to collect donations to the Shipwrecked Mariners' Society.

Sea mines have been used since the 1850's, and are of three types: contact mines, which detonate on contact with a ship's hull, influence mines which react to the noise or magnetic field of a nearby ship, and mines which are operated by some method of remote control.

The distinctive horns on this mine show it is a Royal Navy contact mine from World War 2. It would originally come in two parts: the mine itself, and a "sinker" connected by a cable to the mine. On release, the sinker falls to the sea bed, letting out the cable which tethers the mine to a pre-set depth, just below the surface. Mines which break free of their tethers float, and these still appear from time to time on our shores.

The mine contained up to 450lb of explosives and the effect on a ship hit below the waterline would be devastating. Usually there was little time to evacuate or even send out distress signals. A mine lurks invisible, waiting for a ship to cross its path. The horror for sailors is that a mine can be hit any time of day or night, and total normality can be instantly changed into a desperate battle for survival.

Because of this suddenness and unpredictability, there are few photographs of mine sinkings occurring, but the picture of the French destroyer Bourrasque, mined off Dunkirk the day after Maldon's Pudge came under attack, illustrates the terror of such an event, with sailors and evacuated soldiers desperately jumping for safety.

Mines still represent a danger – UXO (Unexploded Ordnance) is full-time work for companies preparing offshore wind farm sites, and the map kindly supplied by UXO company Ordtek illustrates how our island was ringed with belts of mines in both World Wars, and how (the red blobs) unexploded mines, bombs and shells are still discovered on or near our beaches.

The Germans tended to lay mines from submarines or aircraft, and one of these appeared in the nets of a fishing vessel off the Isle of Wight last year. The video shows the detonation by a Navy team, which caused a measurable earth tremor on the island.

Originally founded in 1839 as The Shipwrecked Fishermen and Mariners' Royal Benevolent Society, the Shipwrecked Mariners' Society gives up to £1.4 million a year in grants to merchant seafarers, fishermen and their dependants to help them through crises. In World War 2 it provided support to thousands of seamen who had been rescued and landed ashore with nothing more than the clothes they stood up in. In recognition of this, the Admiralty gave 200 surplus sea mines to use as collection boxes. 60 remain, among them our historic mine.

As well as placing money in the mine, donations can be made via the link here. The Society also has a "Mine to Mine Challenge" where volunteers (when restrictions are lifted) can visit all the remaining mines.

It is supremely fitting that a terrifying weapon of war, and a key part of our national defence, should be re-purposed to support our heroic seafarers.