For those who have watched last weeks episode (I haven't ......yet.....by the way) you might find this article somewhat interesting - http://www.bbc.co.uk/news/magazine-25019489

Mentioned in the article (para 4) is escape training. This training takes place in a 30m deep tank - SETT - Submarine Escape Training Tank - which is located in Gosport, Hants. There are hatches into the central tank at 10m and 20m and a compartment at the bottom that resembles something like a large dustbin with a lid on the top. This compartment (dustbin) is large enough for 1 person and has another hatch at the bottom through which access is gained to the compartment.

Trainees are required to enter the main tank at the 10m mark where one or two free swimming instructors will greet him/her. After stating name, rank and number to the instructors the trainee is allowed to swim to the surface. Failing to give the said information results in a punch to the guts. The whole point of this exercise is to drum into the trainee that he must at all costs breath out on his way up to the surface.

The exercise is then repeated at the 20m level and successful completion of this is a prerequisite to progressing to the 30m level. The compartment (dustbin) is slowly flooded at which time the pressure inside the compartment equals that of the main tank and the top hatch opens automatically by spring action. Trainees are required to complete two ascents from this level - one free ascent and one suited ascent. At this depth, ones lungs contain 4 times the surface equivalent (compressed of course) and if the student doesn't breath out on the way to the surface the lungs will explode. For this reason divers or free swimmers are located at the 20m and 10m marks and ensure that the trainee is breathing out during the ascent.

The final ascent is a suited ascent. In this instance the trainee wears a Michelin Man type suit. The suit is fitted with an external pressure relief valve on the shoulder and a short connector for inflating the suit from a valve located in the chamber. As water enters and floods the chamber from the bottom the trainee breathes air contained within the suit. At this point the pressure in the suit matches the pressure in the chamber with any over inflation being released via the pressure relief valve. When the top hatch lifts the student starts to rise at which point a belt which he is wearing around the waist is attched to a central strop by a diver/free swimmer. This is to prevent the ascending trainee from flying around the tank in the same way a balloon would if you suddenly let it go without tying a knot in the end. In the sea of course this wouldn't matter as there are no walls with which to collide.
Short video here so you get the general idea - http://youtu.be/rBDlZ7EHx4E

Enjoy - I certainly did.

Size matters - no, never heard of that in the context of submarines.

In the event of damage - um, good question. There are two escape compartments in a submarine, forward and aft. Well three really if you take the conning tower into consideration. You have to look upon a submarine as being cigar shaped - this is the pressure hull - the bit you don't see unless you peer through the various holes in the outer casing. Outside of this (she shape you see) is called the 'casing' and between the two are contained miles of pipes, valves and air tanks. To visualize the escape chamber you have to imagine a large hole drilled through the outer casing into which the escape chamber is pushed through so that the top hatch is now level with the casing top. Because the chamber is something in the order of 6-7 feet tall but the gap between the casing and pressure hull only half of that, part of the escape chamber protrudes through the pressure hull and into the submarine itself.

The first man to enter the escape chamber will do so in dry conditions. Once inside, men still in the sub will open a valve to flood the chamber and when the pressure in the chamber equalizes with the sea outside the top hatch will open and the man then leaves the chamber. There is a winding handle inside the boat to close the top hatch once more. There is also a draining valve/pipe to empty the water from the chamber into the bilges.

Where time necessitates a quicker escape i.e. one man straight after another, there is another method that can be adopted. Fitted around the outer edge of the chamber that is exposed within the boat itself is a fabric curtain which can be lowered to about chest height. This in effect extends the length of the chamber. Here comes the good bit. Dotted around the front and aft compartments are special valves fitted to an airline - this is called the BIBS - Built In Breathing System. Each man in the compartment will don a pair of goggles, a nose clip on the nose and place a breathing regulator into his mouth. Once all are ready the entire compartment is flooded with sea water. The water level will rise in the compartment until the air that has now been pushed up to the compartment roof balances the pressure from the incoming water at which point a state of equilibrium is reached. When the word go is given, men detach themselves from the BIBS system, move forward to the chamber and one by one duck underneath it and swim upwards. Both hatches, outer and inner, are open at this time obviously.

Unfortunately, this last method necessitates men towards the back of the line breathing compressed air far longer than is desirable as there is no possibility of making decompression stops on the way to the surface in the same manner a diver would do so the chances of survival are considerably reduced. It should be remembered, however, that whichever method of underwater escape is chosen it's always best - if circumstances/time allow - to wait for a surface ship to arrive with communications established so that men are not escaping into a totally empty sea.

I did a confined spaces course in a miners training facility at Radstock,
not as much water as your training, but smoke and total darkness.
Interesting was when we got out our air cylinders gave a good indication
of fitness, I had a quarter tank of air left, my shift mate a twenty five year old
female apprentice had only used around a third of her tank.

Quote: Crow wrote in post #5

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Interesting was when we got out our air cylinders gave a good indication of fitness, I had a quarter tank of air left, my shift mate a twenty five year old female apprentice had only used around a third of her tank.

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I used to wear BA at the power station before I retired

I get sky TV, the world at war has been on there several times, along with ww2 in colour and lots of others, one called tanks goes through all the tanks used in ww2.

Morning Roger......oh no, it's early evening here.

Greatly looking forward to the DVD and whilst I am of course aware of both St Nazaire and it's recent significance I've never actually been there as it's one of those places too far East in France that is neither anywhere near the route north-south or north-west routes from where we are - if you get my meaning. Denmark is also a place that neither the OH or I have visited. Norway comes up on the agenda from time to time but for some reason Denmark never seems to get a mention here in the south. Strange.
As you mentioned 'Chariot' in your post it reminded me of something else earlier in my career. My former Commanding Officer at HMS Ganges - the boys training school I attended aged 15 - was non other than Captain BCG Plaice VC - he of Tirpitz fame. http://www.independent.co.uk/news/people...es-1390941.html and several years later, the course instructor for a Leadership Course I was attending was non other than Lt. Ted Briggs who, as an 18 year old signalman at the time, was one of only 3 survivors of HMS Hood. A true officer and a gentleman in every sense - RIP. http://www.dailymail.co.uk/news/article-...ied-age-85.html