The entire 75-strong crew of a British submarine is feared dead after going missing off the south coast of England.

The Affray left Portsmouth last night and submerged about 30 miles south of the Isle of Wight at 2115 BST (2015GMT).

She was due to resurface today at 0830 BST (0730GMT) off Start Point but no surfacing signal was received and her current position is not known.

The code word “subsmash” was sent out to set in place a search and rescue operation.

Search for survivors

Twenty-six ships and submarines from four countries – Britain, France, Belgium and the US – are involved and every available aircraft has joined the search.

All vessels have been asked to look out for survivors, wreckage or oil spills on the surface of the water.

As well as its normal crew of 61, on board, there were two classes of submarine officers under training and a small party of Royal Marines.

According to the Admiralty, they were on a practice war patrol between Portsmouth and Falmouth.

Chance of survival

A senior submarine officer said the crew could survive for up to three days in such a large submarine if they used special oxygen candles stored on board.

The Affray is an A-class submarine designed for service in the Pacific. She was built in 1946 by Cammell Laird and belongs to the 5th Submarine Flotilla.

In January last year, HM Submarine Truculent sank in the Thames Estuary after colliding with another vessel leading to the death of 64 seamen.

Two months later, the Affray was found in 300ft of water 46 miles south of Portland.

It was the worst British submarine accident since the World War II.

The submarine was never recovered because of the depth at which it had sunk and the distance from the coast made a full salvage operation impossible.

A three-month investigation was carried out from the salvage vessel Reclaim using remote-control TV cameras.

The Royal Navy concluded HMS Affray sunk because the snort mast – the tube through which the diesel engine “breathed” while steaming at periscope depth – snapped because of metal fatigue.

This would have let water flood through the tube’s aperture.

Another theory was that a battery had  exploded.