HMS Sandown and HMS Shoreham two Royal Navy mine countermeasures vessels have been operating in Falmouth bay and the Carrick Roads for the past week hunting for dummy mines laid by the Torpedo Recovery Vessel (TRV) Tormentor.

The Sandown Class Single Role Minehunters of which there are 12 ships were designed for hunting and destroying mines and for operating in deep and exposed waters. Mine countermeasures ships have the task of keeping ports and coastal shipping lanes free from the threat of mining. Technological development in mine warfare has meant that mines are now capable of being highly selective as they are capable of targeting a specific ship signature.

Modern mines can be triggered not only by collision but also by the sound of a ship passing through water or by magnetic signature of the ship's hull. The minehunters have to be state of the art vessels built of non-magnetic materials. The mines are detected sonar by bouncing high frequency sound waves off them.

The ships carry remotely operated unmanned submersibles which can identify mines and destroyed by a high explosive charge. In the past decade the Royal Navy has been involved in mine clearance operations in the Falkland Islands, Red Sea and the Gulf.

HMS Shoreham built in 2001 is the last of the class. Another of the class is HMS Penzance. All the ships are constructed of glass reinforced plastic. The MOD decided in 1991 that the TRV's would be converted into practice minelayers when appropriate. Tormentor and her sister ships can carry up to 20 mines.

The Royal Navy has three minecountermeasures squadrons, two based in Portsmouth and one in Faslane.

HM ships Truro, Newlyn, Fowey, Mullion, Newquay, Padstow, Polperro, Portreath, and Saltash were all Aberdare class mine sweepers that saw service after the first World War when a large number of these steam powered ships were commissioned into the Royal Navy.