The Royal Navy's largest ship made its way up the River Thames today as part of a security exercise ahead of the Olympics in London.
The amphibious assault ship, HMS Ocean, will be docked at Greenwich as a precaution against any potential terrorist attacks during the games.
The ship narrowly squeezed through the gap in the flood barrier on the Thames, to form part of Exercise Olympic Guardian, which began on May 2.
The Minstry of Defence said today that four Royal Navy and four army Lynx helicopters will operate from the 21,500-tonne ship.
The ship is fitted with torpedoes, guns and radar and can house 1,100 people.
Small boats operated by marines are also present on the river.
Surface-to-air missiles and Typhoon fighter jets are already stationed around London, and the Navy flagship HMS Bulwark is moored off the south coast for the exercise ahead of the Games.
The journey up the Thames today was made difficult as the ship is is some 35m or so wide.
The gaps in the barrier at the widest points are only around 60m - leaving very little margin for error.
Philip Hammond, the Defence Secretary has denied that sailing the ship up the River Thames was "over the top" in preparation for the Olympic Games.
Speaking today Mr Hammond said Londoners should be reassured by the military presence in the capital,
"These are assets here for their protection and their defence," he said.
"There are no specific threats to the Games at the moment and we hope it stays that way, but if any threats do emerge I hope that the sight of these assets - this ship in particular - will reassure them that we will deal with any security threats in a determined and resilient way."
During the Games the ship will accommodate 300 military personnel who are providing security at nearby Greenwich Park, and engage with Londoners by hosting public visits.
Last year it spent four months operating off the Libyan coast.