TWENTY ships were involved in an intense military exercise off the Cornish coast just days before the mass stranding of dolphins this summer, the Government has confirmed.

The death of 26 dolphins in June, most of them in the shallow waters of Porth Creek on the Roseland, was one of the UK's biggest wildlife tragedies in recent years.

Though up to 200 other dolphins were saved by the intervention of RNLI and wildlife volunteers, campaigners say that 80 more could have been traumatised by the incident.

The Royal Navy at first denied involvement in the disaster, but the Ministry of Defence (MoD) later confirmed it was carrying out exercises in Falmouth Bay just hours before the dolphins beached themselves.

A request to the MoD under the Freedom of Information Act has now revealed that a substantial exercise involving 20 Royal Navy ships and submarines, as well as vessels from foreign Navies, was being conducted in the area in the days leading up to the strandings.

The MoD has confirmed that sonar "dipper" devices were used seven times by Merlin and Lynx helicopter crews in the week before the incident. The mid-frequency sonar used, which is just beyond the range of human hearing, has been associated with strandings of marine life in the past.

Sonar on a similar frequency was also being used by one of the Type 23 Royal Navy frigates on the regular training exercise commonly known as the "Thursday War".

The newly-released data records, in addition, that inert 4.5 inch shells were being fired, as well as Sea Wolf missiles and machine guns.

This confirms reports from local people, who said they heard heavy firing off the Roseland coast for days before the tragedy.

Sarah Dolman, science officer at the Whale and Dolphin Conservation Society, said the new data was "very interesting" and that the sonar activity included the dipping sonar from a Merlin which, at 2-4 kilohertz, is in the range of common dolphin hearing.

Ms Dolman believes the dolphins, which initial post-mortem examinations found to be fit and healthy, stranded because they were fleeing.

"It was probably a flight response from something like a killer whale or something human, like an intense sound source," she said.

"But if there had been killer whales out there, given the numbers of people that were on the water, I think they would have been seen.

"If a number of ships were echo-sounding, it is possible that they could have had a herding effect on the animals. If noise is the cause of these strandings, it is either the sheer number of vessels making noise, causing confusion or herding the animals ashore, or it is some kind of activity on the day."