A Royal Navy nuclear submarine has surfaced at the North Pole after weeks beneath the ice.
HMS Tireless has been a focus for protests
The Plymouth-based HMS Tireless returned to the Arctic Ocean for the first time in eight years for operational exercises with the US navy.
A civilian scientist is with the crew on board to monitor global warming effects on the polar cap.
The submarine has caused controversy and drawn protest in the past and was investigated after a collision at sea.
Scientist Nick Hughes from the Scottish Association for Marine Science (SAMS) is on board the Tireless to take measurements of the thickness of the ice underwater.
The permanent ice pack at the North Pole has retreated 100 miles north in recent years and can thin in the summer to as little as 6ft.
Ice on the Arctic has diminished by 40% in the past 20 years, according to research.
For the past 30 years scientists from SAMS have travelled to the Arctic when a Naval vessel goes so they can monitor the effects of global warming.
The Royal Navy said the vessel's 130 crew will be able to stretch their legs and take in the extraordinary beauty of the Arctic wilderness during the surfacing.
The last time the craft surfaced was at the French port of Brest in February.
A Royal Navy spokesman said: "They've been crammed on board the sub under the ice for weeks so they'll be dying to go for a walkabout.
"Let's hope there's not too many polar bears about."
A previous US submarine mission crew had to watch in amazement as one inquisitive bear chewed the fin and external casing of their vessel.
The Tireless has caused controversy in the past.
In May 2003 it was taken to Scotland for repairs and prompted a Ministry of Defence inquiry after it collided with an object at sea.
The craft has also been a target for anti-nuclear protesters in Plymouth who attempted to break into a naval base in 2003.
In 2001, its presence in Gibraltar put a strain on relations with Spain and caused outrage among environmentalists.