"A Navy helicopter was using controversial sonar equipment off the Cornish coast days before 26 dolphins died in a mass stranding.
Officials at the Ministry of Defence admitted last night that the sonar "dipper", designed to hunt submarines, had been used by a Merlin helicopter on training exercise.
The mass dolphin stranding was the biggest in Britain for 30 years.
Four days later, the dolphins beached in the shallow Fal and Percuil rivers 60 miles away near Falmouth. The mass stranding last Monday was the biggest in Britain for 30 years.
Conservation groups want a full investigation. Marine wildlife and underwater acoustics experts said loud pulses from the sonar may have scared or confused the common dolphins into Falmouth Bay, where they became disorientated. An investigation by The Sunday Telegraph discovered that the sonar was being used as part of an exercise involving the nuclear-powered submarine Torbay and a number of surface warships."