What is life like aboard a hunter-killer submarine?

We approach HMS TURBULENT in a launch from the Kyle of Lochalsh. It is a still, cold, sunny autumn evening, but we are quite close up before we see her. Most of the bulk of her 85-metre casing sits below the water, and when she's running on the surface, you can see only the fin, the rudder, and the uppermost arc of the barrel of her body, sleek with water.

And then, there she is. She looks, from the side, streaming bubbles, like a whale with a shed on top. But some whale. Some shed. TURBULENT is a nuclear-powered hunter-killer submarine, capable of spending 90 days at a depth of more than 300 metres without support.

That is, she could dive, travel from Plymouth to the Falklands, spend seven weeks in theatre, and return to Plymouth without ever poking her fin above water. She's ready to go anywhere in the world at 48 hours' notice.

She can act against ships, other submarines, can reconnoitre coastlines and intercept radio signals, and can insert and remove special forces.

Originally designed, 20 years ago, to hunt Russian submarines, she has since been adapted to fire cruise missiles and, in the war against Iraq, TURBULENT sat in the Gulf (she spent 10 months at sea) and fired on Baghdad.

That's the Boys' Own stuff. But it's tempered once you've been hauled up a rope ladder on to the casing and climbed down into the main hatch. The first thing you notice as you leave the outer air is the smell - a powerful commingling of oil, rubber, and the ghosts of farts.

"That's a real submarine smell," said one of my companions with approval - he's a former submariner - as we walked into the wardroom, the naval equivalent of an Officers' Mess. After a long time at sea, apparently, the smell takes three washes to leave your clothes clean.

Submariners adapt to it. One I spoke to remembers surfacing in the Arctic after weeks below, climbing the conning tower and finding the taste of fresh air so oppressive he was physically sick.

The second thing you notice is the space - or lack of it. The corridors are narrow enough that two men have to turn side-on to squeeze past. The ceilings are covered with piping, valves, and dials. Everything seems to be labelled. And everywhere, there are wall-mounted boxes containing firefighting gear, emergency kit, tools; pipes in the ceiling bristle with brass nozzles for the emergency breathing system.

From a galley the size of a walk-in wardrobe, two chefs produce four hot meals a day, every day, for a ship's company of 132. (And, crucial to morale, these are good meals - I've seldom eaten so well for a sustained period, or so much.)

The men grab what sleep they can "racked" three deep in dark cabins, with barely a foot of space between the opposing rows of bunks. They "hot-bunk" - sharing the use of a rack with a shipmate working an alternate watch.

Sometimes they get "coffin dreams" - nightmares from which they come to in the close dark, not knowing where they are, and panic.

I was racked in the "bomb shop" in the basement of the ship, where sleepers wriggle on to shallow, fibreglass pallets in less than two feet of crawlspace, under pointed fixtures designed to hold heavy weapons in place (my scalp throbbed with self-inflicted contusions).

If I say I woke up feeling a million dollars, it was because my left arm butted up against £1.25 million of Tomahawk missile - a metal tree-trunk stuffed with rocket fuel and high explosive. The bomb shop contains eight or nine of these, not to mention a good few Spearfish torpedoes. Smoking is discouraged.

Does this sound like hell on water? Perhaps. But what I found among almost every member of the ship's company I spoke to during the four days I accompanied them on their transit from the west coast of Scotland through the Irish Sea to Plymouth, was a pride and pleasure in the life - and the sort of self-confidence that you get from being very, very good at a difficult job.

Ask a weapons engineer about the missiles, and you'll get a mini-lecture on different sorts of rocket fuel (the clear one smells not of pear-drops but Ralgex; the darker one is more the colour of molasses). The headphoned teenager manning the sonar can discern the "clicks and bangs" of a diesel submarine from the whistle of dolphins riding the bow wave; the difference in propeller sound between frigate and container ship, and the drag of a trawler's net on the seabed.

And there are moments of great beauty. When the submarine is running on the surface, you can stand on the bridge, at the top of the fin, looking down as water pours over the surface of the nose, ripped ragged by the gaps in the soundproof black tiling. At night, in a high winter sea, says the captain, Andy Coles, this can feel like the loneliest place on earth - with great icy spouts of water known as "goffers" surging up the front of the fin, and drenching the man on watch to the skin.

Lt Paddy Ryan, who as CASO (Casing Officer) is frequently that man, describes one of the talents for which he most admires his father, a former submarine commander: "The sea can be pouring over you into the bridge, and he can still keep a cigarette going."

When Paddy, educated at Sherborne and Durham, "got his Dolphins" this year he became the first fourth-generation submariner. His great-grandfather died when his submarine hit a mine in the First World War and his grandfather was aboard Thetis, which was lost in Liverpool Bay in 1939, just before the Second.

In order to gain your Dolphins - to qualify as a submariner - you have to know the whole boat, top to bottom. Until then, like visiting journalists, you are categorised as an "oxygen thief". Like a taxi driver doing the Knowledge, you must prove you can identify unhesitatingly every one of more than 500 valves and widgets, and know exactly what does what.

In case of fire, leakage or hydraulic burst, any member of a ship's company who sees it must know how to deal with it. Crew members multi-task: the leading steward, Jamie Harrison, is one moment serving the officers their supper and the next, his tattooed arms steady at the wheel, piloting the submarine.

While I was aboard, four new submariners qualified; they collected their Dolphins in a brisk, informal ceremony in the junior rates' mess. "There aren't that many submariners in the world," Cdr Coles told them. "Welcome to the club. Wear your Dolphins with pride - they do mean something."

Then, each man, as is traditional, drained a tot of rum and caught the metal badge at the bottom of it between his teeth. "Waaauuugh," said 25-year-old Andy Witts. "That's a bit tart. I once swallowed some white spirit by accident, and it had nothing on this." Beside him, a shipmate only 17 years old caught his Dolphins without wincing - his tot was of Coca-Cola.

It is notoriously easy for civilians to romanticise military life. Living amid the permanent noise of tannoys and vacuum cleaners and scurrying shipmates and watershots (dry-firing of the torpedo tubes - it sounds exactly as the real thing does; a whoomping at the bottom of the boat) is hardly romantic.

But I arrived expecting to see a starchy, martinet-thronged world of snapping and saluting and clicked heels - and saw instead a crew basically having a ball. Cdr Coles is still cock-a-hoop about "sinking" another T-class boat, Torbay, in a recent training exercise. Skills that in wartime will be vital to life and death are, in peacetime, at the service of games and drills - imaginary torpedoes sink imaginary submarines. Cdr Coles's style with his crew combines warmth with steel.

The closeness of quarters and companionship that characterises submarine life translates itself into a sort of clannishness. Submariners, even within the Royal Navy, have always been set somewhat apart. During the Cold War, the necessarily covert nature of their operations meant they could not tell anyone much about what they did. To some, their invisibility gave them a mystique; colleagues in general service, they say, sometimes saw them as snooty.

Submariners talk a lot about sleep. The crew who work forward of the nuclear reactor - in the control room, on the sonar or the weapons systems - are known by an unprintable rhyming sobriquet (it contains the word "front" rather than "for'ard"), and do shifts, six hours on, six off. Those aft - "bin bags", because the overalls they wear in engine-room heat of up to 55C make them look like dustmen - work a slightly different rota. But for all of them, the precious moments between coming off duty and your next "shake" awake are crucial.

The time not spent sleeping or on watch is whiled away telling stories ("spinning dits"), watching DVDs, playing video games or, in the case of the more assiduous, studying for courses, and drinking cup after cup of hot drinks ("wets"). The atmosphere of mess-room life, with its confinement, its constant salty banter, rituals and routines, risk of boredom, is in some ways close to that of a boys' boarding school, even down to the evolution of a private language - "Jackspeak" - and arcane superstitions (oxtail soup, I'm told, is considered bad luck).

But this is a boys' boarding school that can snap, suddenly, into seriousness. If a sonar operator records a close contact with a fishing vessel, the captain can be at the periscope in a moment. During drills for firefighting and "attack teams", and preparations for diving, orders and queries snap back through the boat with drilled precision: "Starboard 15...Steer 153...Going right 153...All positions stand by...Stand clear search...Search going up...Breaking...Clear..."

More than one submariner I spoke to talked of leading two lives. Subject to long and unpredictable absences from wives and children, the ship's company forms a sort of parallel family.

Those who work on the Vanguard class boats, which carry the nuclear deterrent - "bomber queens" - are yet more isolated from their families. They spend months dived in deep ocean, and for security reasons can't contact their families except to receive, once a week, a censored 40-word "familygram". Yet marriages survive.

Lt-Cdr Nigel Reece was expecting his first child to be born this week, the day after we arrived in Plymouth. His wife had sent him to sea with a copy of The Baby Whisperer as homework. The longest-serving of the ship's company, Chief "Snowy" Sleet, joined the Navy at 16. At 44, he counts in terms of the submarine service as a grand old man. His marriage has survived 23 years. Another young submariner is planning to propose to his girlfriend this very weekend.

Whenever the boat surfaces, the men take turns climbing up into the fin, where they crouch among the stalks of the periscopes and look for a signal on their mobile phones.

Only once did the men-without-women stereotype cause a moment of anxiety. "Watch out for the Captain," one officer I won't name told me, not long after I joined the boat. "He's a notorious timbershifter. If you're not careful, he'll get you in the wardroom and give you an eight-piece dicking." Reader, for all my open-mindedness, I was afraid. I need not have been. They were talking about an ancient naval board-game called Uckers. It's best thought of as a sort of combat ludo, though the rules of Uckers tend to be the subject of heated negotiation during the course of the game.

It, too, has its own vocabulary; of "blobs", "eased blobs" and "mixy parties". "Timbershifting" is the practice of accidentally mis-counting, to your own advantage, the number of squares your piece travels. "Eight-piece dicking" is the technical term for a severe defeat in which your opponent finishes while all your bits are still on the board.

I have seldom met a man more affable, capable and professional than Cdr Andrew Coles of HMS TURBULENT. But the record should also show that I nevertheless suspect him of being a six-throwing, timbershifting, ludo-playing bastard.

Cdr Coles would doubtless be the first to chide me with an established truth: "Submariners never cheat and seldom lie."

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