Four Royal Navy mine countermeasures ships are due to leave Portsmouth today for a transatlantic crossing and a series of exercises with forces of six other nations.

HM ships Pembroke, Walney, Sandown and Middleton are heading west to the United States to hone their minehunting skills off the eastern seaboard in Exercse Rapid Alliance, a major amphibious exercise led by the United States and including forces from Canada, the Netherlands, France, Germany and Australia.

The deployment is part of the Royal Navy’s Aurora task group, the largest force of ships assembled since Operation Telic last year.

The training will be interspersed with goodwill visits to ports in the Azores, Bermuda, Virginia, Massachusetts, Nova Scotia and Newfoundland.

Cdr Peter Williams, the man in charge of the task group, said: “This deployment presents a rare opportunity for the minehunters to work alongside their American colleagues on their own turf.

“The combination of a stimulating large-scale exercise and several exciting port visits make the trip hugely attractive.”

Royal Fleet Auxiliary landing ship Sir Bedivere will accompany the MCMVs across the Atlantic as the command platform for the exercise, and will also provide engineering support for the four ships, which are expected to return to Portsmouth in early July.

Pembroke, Walney and Sandown are all Sandown-class ships, known as single-role minehunters because of the role they fulfil.

These ships are equipped with sophisticated sonar equipment, which allows them to spot suspicious objects on the seabed. A diver or a remote-controlled submersible (the “yellow submarine”, because of its colour) is then deployed to further investigate and, if necessary, dispose of the object with explosives.

The other ship, HMS Middleton, is a Hunt-class MCMV, which is also capable of hunting mines by pinpointing them, but was also built to be able to sweep in the traditional style, using cutting wires to address buoyant mines or transmitting devices which mimic passing ships, causing acoustic or magnetic mines to detonate harmlessly.