Prince William has taken part in early-morning manoeuvres near the River Clyde while on a visit to the home of the UK's nuclear deterrent.
The prince took to the water with Royal Marines based at Faslane, home to the fleet of Trident submarines.
Dressed in a dark blue immersion suit and dark green life-jacket, he went out in an offshore raiding craft with four Royal Marines.
As the sun rose, they sped up the Gare Loch accompanied by other craft.
William stood at the back of the offshore raiding craft (ORC) with three Marines while one manned a gun at the front.
They carried out manoeuvres at speed for about 10 minutes around MV Adamant, which was idling in the loch.
ORCs are used for the protection of submarines and surface craft moving in and out of the base.
Faslane is the first base in the UK to have the fleet of two boats, which were delivered two weeks ago.
They can travel at up to 40 knots and are equipped with two machine guns and a grenade launcher.
The 30ft (9.1m) boats weigh 4.5 tons.
William, 25, is visiting Faslane in his capacity as Commodore in Chief Scotland and Submarines.
The trip was designed to give him a chance to meet Royal Navy personnel and their families.
The prince, Second Lieutenant with the Blues and Royals Household Cavalry regiment in the Army, will undertake secondment with the Royal Navy and RAF next year.
Later William took part in the dramatic boarding operation with other Royal Marines.
Armed commandos boarded the target vessel simultaneously from a boat and helicopter in a meticulously timed exercise. Major Woody Page, a squadron commander with the Fleet Protection Unit at HMNB Clyde, said they were pleased William was visiting. He said: "We are delighted he is here. We had a good dinner last night and he seemed very relaxed. It's nice to see him up here with the Royal Navy."
The Major added: "He is an officer and he will probably appreciate the experience and opportunity to talk to the boys."
Back on dry land, William went on to meet Naval families, local community groups and youth groups when he opened a refurbished room at the Drumfork Club in Helensburgh, a social club for Naval families.