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UNKNOWN MALE:'The submarine's huge. It's 100m long, it's three decks deep, there is no inch of the submarine that is similar to another inch of it. I would definitely put it in the same league as a space shuttle, or projects of that size.'

UNKNOWN MALE:To my mind, this is a 7,000 ton Swiss watch. There are stages when it's like blacksmithing, and there are stages when it's like brain surgery.

NARRATOR:'The Astute is one of the most technologically-advanced machines in the world.

NARRATOR:'Computer aided design and manufacturing, or CAD/CAM, is a tool that allows for accuracy, and essentially to try ideas out, saving money and time. It allows for continual evaluation, analysis, and redesign where needed.

NARRATOR:'When building something as complex and expensive as a nuclear submarine this process is essential.

NARRATOR:'The naval architecture team are some of the best in the world.'

ROB RITCHIE:The submarine is designed to operate in a very hostile environment, which is under the sea, at pressure. It's a salty environment, it wants to corrode. And at the same time, it has to keep its crew, of 97 crew, safe,

ROB RITCHIE:for about a three-month period without surfacing.

ROB RITCHIE:So it has to make its own air, makes its own water, carries its own food. And it also has to operate as a war-fighting machine as well.

NARRATOR:'With around 600 people involved in the design process alone, this is one of the largest concentrations of such expertise there is.'

CAD/CAM DESIGNER #1:This computer simulation shows us the whole submarine's response to an underwater shock, so an explosion of some sort of some underwater weapon.

CAD/CAM DESIGNER #1:It helps us figure out what stresses a boat would see, the accelerations equipment may see in the boats, so it helps us design the boat to survive, basically.

NARRATOR:'These designers are potentially saving millions of pounds. It would be far more costly if things were built and didn't work out.'

CAD/CAM DESIGNER #2:The main reason for us using this computer simulation process is it's too expensive and too difficult to do this testing in real life on real submarines.

NARRATOR:'Virtual testing like this, allowing infinite changes and able to store vast amounts of information is a vital part of the design process.'

PETER BROADBENT:We build it first inside a computer aided model, so we build it, lay it all out to make sure people can operate it

PETER BROADBENT:and also it can meet its functional performances as well.

PETER BROADBENT:'Once we've done that then we move on to actually issuing all the drawings, so all the drawings originate from our computer aided model. So them drawings then go to our operation department who actually build the Astute.'

NARRATOR:'The Astute contains more than a million individual components, designed on a computer but built by hand.'