Six Royal Navy vessels have been dispatched to Lebanon, where they may be called into action to rescue stranded Britons. What are their capabilities?
The UK's most powerful warship, based in Portsmouth and captained by Commodore Robert Cooling.
The Ministry of Defence says the ship is an "important enabler of foreign policy".
"No other platform provides the flexibility, power projection capability and command and control facilities of an aircraft carrier," it says.
Built at Tyneside's Swan Hunter shipyard, it has the nickname Lusty and a full complement of 1,110 - 726 ship's company and 384 air personnel
The 22,000 tonne aircraft carrier is 210m in length, sails at up to 30 knots and has a flight deck the size of two football pitches and the length of 23 double-decker buses
Equipped with three Goalkeeper anti-aircraft/anti-missile
systems and two 20mm close range guns, it can carry a range of aircraft including Harrier jets and Sea King, Chinook and Merlin helicopters
Since being commissioned in 1982, it has travelled more than 600,000 nautical miles - the equivalent of 24 times around the world
It has been involved in policing the no-fly zone over southern Iraq, disaster relief after floods in Mozambique, and supporting operations in Sierra Leone and Afghanistan
It is the fifth ship to bear the name Illustrious and had a two-year £120 million refit, completed in December 2004
Ship motto is Vox Non Incerta, meaning "no uncertain voice"
One of the most technologically-advanced warships the world
has ever seen.
It was built by BAE Systems in Barrow-in-Furness, Cumbria, and entered service in 2004. It is based at Devonport.
Carries up to 700 personnel, two helicopters and eight landing craft, and has the technology to function as a floating battle command centre
Weighing 18,500 tonnes, it is one of two amphibious assault ships in the Royal Navy
The 176m vessel's flight deck can accommodate two Merlin helicopters, and a large floodable dock holds four large landing craft, with four more secured to the sides of the ship
Acts as the platform for 4 Assault Squadron of the Marines and is described as "the most up to date amphibious platform in the Royal Navy"
Can conduct reconnaissance of beaches, landing points and waterways in preparation for amphibious operations, and prepare and control two separate beaches during amphibious operations
Armed with two 20mm close-range guns, four machine-gun positions and Goalkeeper anti-missile systems
A type 42 destroyer, the present HMS Gloucester was one of the last four of the class to be built.
A Gulf War veteran, the Portsmouth-based Gloucester made history on 25 February 1991 when it became the first Royal Navy warship to shoot down an enemy missile in combat.
The destroyer was escorting the USS Missouri close to the Kuwaiti coast when an Iraqi Seersucker missile was fired against the American vessel. In less than 90 seconds Gloucester had destroyed it with two Sea Darts.
HMS Gloucester was built by Vosper Thorneycroft at Woolston, Southampton, and launched on 2 November 1982 by the Duchess of Gloucester
Captained by Commander Mike Paterson, it is powered by four Rolls-Royce gas turbines - two Olympus engines give it maximum speed of around 30 knots, while the two smaller Tynes are used for cruising
Designed principally as an area air defence ship, Gloucester provides protective cover for itself and a task group with British Aerospace-manufactured Sea Dart surface-to-air missiles
Type 42 destroyers have proved versatile ships in a variety of roles since their introduction, and include in their armoury a 4.5in gun, torpedoes and helicopter-launched Sea Skua air to surface missiles
The ship's motto is "Prorsum" which means Onwards
Another Type 42 destroyer, HMS York was the last of its type to be built for the Royal Navy.
Launched in 1982 and accepted into service in March 1985, it is the 12th ship in the Royal Navy to bear the name
Now based in Portsmouth, it was built by Swan Hunter shipbuilders in Wallsend, Tyne and Wear
Its deployments have included the Gulf, the Falkland Islands and operations in the Adriatic
An extensive refit in 1994 saw new radars fitted - these were the Type 996 medium-range target indication radar and the Type 1007 navigation radar
The command system was modernised with the introduction of a new computer and display system. A replacement 4.5in Mk 8 gun and new Sea Dart launchers were also fitted
The ship's motto "Bon Espoir" means Good Hope and was the motto of Edmund Langley, the First Duke of York 1341-1402, who was the fifth son of Edward III
York's funnel badge, a red cross with lions passant, is from the coat of arms of the City of York
HMS ST ALBANS
A type 23 frigate, HMS St Albans is the 16 and final ship in the 'Duke' class of frigates in the Royal Navy.
The Dukes were originally conceived as Atlantic anti-submarine hunters for the Cold War which ended as the first two of the class, HMS Norfolk and Argyll, were entering service.
Instead, the frigates have become the workhorses of the fleet around the globe, called on to perform defence diplomacy, gunfire support and anti-smuggling operations as well as their intended role.
The sixth ship to bear the name, HMS St Albans is captained by Commander Steve Dainton, and was launched on the 6 May 2000 by its builder, BAE Systems, at Scotstoun. It was accepted by the Royal Navy in November 2001
The 4,900-tonne vessel carries up to 185 troops and was on its first mission, Operation Aquila - a counter-terrorism and piracy operation in the Indian Ocean - when it received the call to Lebanon
Equipped with Vertical launch Sea Wolf anti-missiles missile system; Harpoon anti-ship missile, 4.5in Mk 8 main gun, 30mm cannons and 7.62mm machine guns and Stingray torpedo and a Lynx or Merlin helicopter
RFA FORT VICTORIA
Part of the civilian-manned Royal Fleet Auxiliary service, Fort Victoria is designated as an Auxiliary Oiler Replenishment (AOR) ship, but is often described as a "floating warehouse".
Named after a fort on the Isle of Wight, Fort Victoria was ordered from Harland and Wolff in 1986, and was launched in 1990. However, various problems with the construction of the vessel meant that it was not delivered until 1993
On board are
240 men and women from the RFA, a Royal Marines boarding team and the Royal Navy, including members of 814 Naval Air Squadron and Merlin helicopters. Commanding officer is Captain Bill Walworth
Fort Victoria has four dual-purpose abeam replenishment rigs, which means it can transfer both fuel and stores to two ships at the same time
The ship can also transfer stores from ship-to-ship or ashore by helicopter
Fort Victoria has a flight deck served by three hangars, and has repair facilities on board for Merlin helicopters
The ship was deployed as part of Operation Aquila before being sent to Lebanon. She was there supporting, among others, HMS Illustrious and HMS Gloucester
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