HMS Triumph: Life on board a Royal Navy submarine
HMS Triumph is one of the Royal Navy's Trafalgar class submarines, using its stealth on counter-piracy, anti-terrorism and narcotics operations. BBC defence correspondent Jonathan Beale has had exclusive access to the confined space where 120 crew members serve.
It's called the "silent service" for a reason. Months on end spent below the surface of the sea, without any daylight for weeks at a time, living in cramped conditions, and little communication with the outside world.
For the crew of HMS Triumph, one of the Royal Navy's five nuclear-powered, hunter killer submarines, it's been an endurance challenge. A test of their resilience. They've been on deployment for the best part of a year: 323 days on operations; with 257 days at sea and 93 of them on "silent patrol".
Since November they've been travelling "East of Suez". Patrolling the region's hotspots from Somalia to Yemen and through the Strait of Hormuz - the narrow stretch of water which Iran has threatened to close.
Triumph's Captain, Commander Rob Dunn, likens their role to being "the special forces of the maritime world". He says they've been involved in counter-piracy, anti-terrorism and narcotics operations as well as "regional engagement".
But he adds that "we can't comment on a lot of what we do" other than doing what submarines do best: "utilising their inherent stealth". The mission is as mysterious as the submarine's precise movements.
HMS Triumph is loaded with Spearfish torpedoes and cruise missiles. Last year, she launched the first UK strikes on Libya, firing more than a dozen Tomahawks.
Less well known was the work she did to stop Colonel Gaddafi's forces from mining Misrata harbour, and chasing their speed boats - loaded with explosives - through treacherous shallow waters.
Longest solo journey
Triumph can also gather intelligence using her powerful sonar. Shaped like a cigar, she measures 280 feet long (85m) and just 32 feet wide. She is covered in sonar absorbing tiles making it difficult for other vessels to detect her movements.
Triumph's own nuclear plant helps generate her own power, fresh water and air without the need to refuel. In 1993 she completed a 41,000 mile (66,000km) journey to Australia, mostly submerged and without support.
It's still the longest solo journey in the history of the Royal Navy. It would take just 14 days for the submarine to reach the Falkland Islands from her home port of Plymouth.
Most of the Trafalgar class submarine is taken up with machinery, leaving little living and working space for her 120 crew.
Conditions are cramped with little privacy. Cabins, smaller than a hotel room, sleep up to 30 men. There are just 99 beds in total, meaning that some of the junior ratings have to "hot bunk". When one submariner leaves his bed for duty, another finishing his watch will take his place.
There are even bunks, no bigger than coffins, set up alongside the cruise missiles in the weapons stowage room.
'The dog's ok'
The only fuel the crew needs to replenish is their food - essential to keeping up morale. One small kitchen and three chefs provide four meals a day for the different watches.
Sometimes you only know the day of the week by what's on the menu: Wednesday's curry night, Friday fish and chips, and on Sunday there's a traditional British roast. Leading Chef Wayne Claridge says that if the food's "rubbish", morale suffers. He says he can either be the most, or least popular person on the boat.
News from home can also keep spirits up. But contact is limited. On a "silent patrol" the only communication the crew receives is a 40-word weekly message from home. Chief Petty Officer Simon Johnson says it's often very simple. He describes it as "Dad's ok, the dog's ok and no bad news".
Senior officers can vet the "family-grams" to protect the crew from upsets. A number have suffered bereavements while out on patrol. Some opt not to be told until they're in a position to go home. When the submarine surfaces they can put up what the crew call "the happy mast". It gives them a connection to the internet to receive and send emails.
For all the discomforts, the long hours, and no days off, there is an incentive - extra pay. A submariner receives at least £20 a day more than his counterpart on a "skimmer" - their term for a surface ship.
Still, there are huge sacrifices - not least in losing touch with what's happening back home. Most of Triumph's crew have missed out on this year's landmark events such as the Queen's Diamond Jubilee and the opening ceremony of the Olympics. But it is being away from family and friends that's the hardest to bear.
With the Royal Navy having fewer submarines, deployments are getting longer and harder. Chief Petty Officer Paul Foran says the greatest lesson a submariner can learn is tolerance.
If you don't get on with someone, you still have to try your hardest, he says.