Two crew members of an American submarine have died after falling overboard in Plymouth Sound.
The nuclear-powered submarine is based at Norfolk, Virginia
They were among four crewmen who were working in poor weather on the outside casing of the USS Minneapolis-St Paul off the Devon coast.
A rescue helicopter from RNAS Culdrose, a tug boat and a lifeboat were sent to the men's aid while they were tied on to the side of the 110m (362ft) vessel.
The sailors were brought back to shore and taken by ambulance to hospital.
A spokesman for Brixham Coastguard said: "The four got into difficulties while on the outer casing of the submarine.
"They were unable to get back on board, they were tied on but getting battered about by the weather."
The submarine was getting under way from the Devonport naval base
Two men appeared to be breathing with difficulty and were given CPR as they approached the shore.
They were taken to Derriford hospital in Plymouth, where two of the servicemen were pronounced dead.
The two other men were transferred to the sick bay at HMS Drake and later released.
A Devon and Cornwall Police spokesman confirmed two of the crew were pronounced dead on Friday afternoon and the coroner had been informed.
A joint investigation by police, the Ministry of Defence (MoD) and the United States Navy has begun.
A US Navy spokesman confirmed four sailors from the vessel had fallen overboard as it was getting under way from Devonport naval base.
"The names of the sailors are being withheld until their next of kin have been informed.
Ships have to go through the Sound to get to the city's naval base
"Our thoughts and sympathies are first and foremost with the families and loved ones of the sailors who sadly lost their lives today in this incident."
He said the vessel had just completed a week long visit to Plymouth.
The American nuclear-powered submarine, which is based in Norfolk, Virginia, was leaving the harbour at the time of the incident and has since continued on its journey.
It has been operating under the US Sixth Fleet since October.
The MoD said it could not comment on what the vessel was doing in British waters.
However, submarines have to travel through the Sound to get to and from the city's Devonport Naval Base.
The submarine, which has a complement of 137 officers and enlisted crew, can reach speeds exceeding 25 knots (29mph). Its weapons include torpedoes and Tomahawk cruise missiles.