By Peter Marshall
BBC North West Tonight
HMS Vengeance is one of four Trident carriers
HM Naval Base Clyde is simple to find they say.
Just head out of Glasgow and follow the barbed wire. Miles of it. But considering what the base contains you would expect it to be pretty well guarded.
The Royal Navy fails to mention the anti-Trident peace camp that runs along the other side of the main road up to the Faslane base - a colourful collection of shanty-like sheds and caravans - just as striking as the barbed wire.
We're here to see something seldom seen - one of the four hulking submarines that carry the UK's independent nuclear deterrent - Trident.
The boat currently in dock is HMS Vengeance, built in Barrow, Cumbria, and bigger than you could imagine.
So big that one of the journalists who has travelled miles for a rare glimpse inside has an attack of vertigo as she prepares to descend the ladder into the depths of the sub. She never makes it on board.
No women work on board
You cannot look at the hulking black shape of HMS Vengeance without hearing, in your mind, the score from Jaws.
It looks lethal, and it is. On board we are told it has the destructive capability to return the modern world to the Middle Ages. Sixteen Trident missiles each capable of delivering up to 12 warheads.
It does not bear thinking about.
The 135-strong crew, of course, have to think about it. They lie in cramped bunks, knowing that a few feet beyond their pillows are umpteen nuclear bombs.
They seem happy with the safety arrangements, and totally convinced that their boat plays a vital role in global security.
Let's put global security to one side and talk baked beans. Vengeance is being loaded ready for another trip to sea.
Food is the only thing that limits her time under water, and while I'm taking a good look around the corridors are crammed with tins and tins of baked beans, and pickled onions... and pickled red cabbage.
Luckily, the craft can produce fresh water from seawater. One gets the impression they will need it.
They say a submarine is like Dr Who's Tardis - only in reverse - huge on the outside and tiny and cramped inside.
The crew's sleeping quarters are shared
As subs go they do not come much bigger than HMS Vengeance, but even here the crew, many from north-west England, still has to carry out the rather unsettling practice of "hot-bunking".
There are not enough beds to go round, so at the end of your shift you may have to leap into a bunk that has just been vacated by a colleague. It takes a certain sort of chap to be a submariner.
It is a men-only environment, women are not allowed to join.
The perks? The banter is good, they say. The pay is good too, higher than in other parts of the Royal Navy. But it has to be. Separation from families is the real drawback, I'm told.
While out at sea they can lose loved ones back home and not be told about it for ages. Bad news can be kept back.
Not everyone could be a submariner. I was on the boat for a matter of hours and already I know I could not do it for a living. But all those I spoke with loved the job, were committed to it and were highly professional.
Say what you like about the rights and wrongs of the nuclear deterrent, but it exists, and it is a comfort to know that the men looking after it on HMS Vengeance know their business.