Royal Navy warship HMS Ocean has arrived in London to take part in security drills ahead of the Olympics.
The ship completes the military presence in London for Operation Olympic Guardian.
Typhoon jets have also been stationed at RAF Northolt, puma helicopters are operating from Ilford, and ground based air defences are being tested with dummy missiles at six sites across London.
Defence Secretary Philip Hammond was taken on board HMS Ocean by a landing craft, as it made its way up the Thames to Greenwich.
He addressed the ship's company in the hangar before taking a tour of the vessel.
"There are no specific threats to the Olympic Games but we're going to have very large numbers of foreign visitors in London."
"The world's eyes will be upon us and we want to make absolute sure that we do everything to maintain the security and safety of the Games.
"Ocean's presence on the Thames, I hope, will be a very great reassurance to people attending the Games."
Captain Andrew Betton, Commanding Officer of HMS Ocean, said:
“As a former Commanding Officer of HMS Westminster, a ship with such great links to London, I am particularly pleased to be bringing HMS Ocean to Greenwich to be part of the Olympics, a truly once in a generation event.
“HMS Ocean is the largest ship in the Royal Navy and is ideally suited to the task of supporting the Police in providing security for the world’s largest, most famous sporting event.
“Everyone onboard is proud to be involved in the Olympic Games and thrilled to bring our ship into the centre of London for all to see at such an important and exciting time for the city.”
HMS Ocean is en route to a position in the Thames near Greenwich from where it will be taking part in an Olympic training exercise. It is the largest warship in the Navy’s surface fleet and the closest thing Britain currently has to an aircraft carrier.
- An amphibious assault ship - designed to deliver troops to the centre of the action
- Room for six helicopters on deck and many more below
- Was deployed as part of the NATO air blockade of Libya
- Will provide a barracks for up to 1,000 soldiers during the Olympics
- Can launch fast boast and helicopters
Our correspondent Simon Harris is on board HMS Ocean, as the warship makes its way up the Thames.
It is being sailed towards London as part of a military exercise being carried out in preparation for the Olympics.
A Royal Navy Lynx helicopter lands on HMS Ocean, as Britain's largest warship sails up towards London.