The Royal Navy's largest ship will sail up the River Thames ahead of a major security exercise in preparation for the Olympic Games.
HMS Ocean will berth at Greenwich in east London where it will act as a launch pad for eight Lynx helicopters and a base for Royal Marine snipers. It is the final phase of the exercise named Olympic Guardian, which began earlier this week in Weymouth and in the airspace over the capital.
Smaller crafts and patrol boats will accompany the ship as part of the maritime security plan.
The snipers have extensive experience of shooting the engines of fast vessels in the Royal Navy's fight against the drug trade in the Caribbean. Ocean will travel up the Thames before attempting a complicated 180-degree turn as it reaches its destination.
The warship is 38 metres wide, and Captain Andrew Betton will carefully guide it through "challenging" gaps of just 60 metres. He said the ship would focus on air security over the weekend, with river operations taking place between Tuesday and Thursday next week.
"That will stretch all elements of Ocean's contribution to the security plan, and then I hope assure the security organisation that we are ready to provide the envelope required for the Olympic Games themselves," he said.
Capt Betton said the ship would provide vital assistance in stopping any potential threats on the river.
"The versatility and manoeuvrability of helicopters allows them to get to the scene of action very swiftly to identify and to divert any surface vessels that are heading up the Thames, to ascertain their intentions and if necessary take action," he added.
Lieutenant Mike Robertson from 661 Squadron, who will fly Army Lynx helicopters from Ocean, said there were "a huge number of threats" that the military could potentially face. His unit returned from Afghanistan only five months ago, and he described the transition to protecting London as "very challenging".
Lt Robertson added: "I'm very excited as are all the squadron to be part of the Olympic Games. It's a once in a lifetime opportunity to be part of the greatest show on Earth, especially in your home country."