First in its class

The Royal Navy's new submarines are the result of one of the country's biggest engineering projects. E&T takes a look inside.

When HMS Astute begins sea trials later this year, its crew will get a taste of life in the biggest and most powerful attack submarine ever to be built for the Royal Navy.

The first in a class of next-generation craft that bears its name, and claimed to be a more complex challenge than the space shuttle, the Astute design involved production of more than 7,000 design drawings. The result, despite being about a third larger than the Trafalgar Class that it will replace, requires a much smaller ship's company and is said by prime contractor BAE Systems Submarine Solutions to have lower running costs.

A nuclear submarine is typically three times more densely packed with equipment than a surface ship, so spatial constraints are enormous. The thousands of sub-systems built into Astute rely on 100km of cabling, 10km of pipework, more than a million individual components and over five million lines of software code.

Three more vessels, HMS Ambush, HMS Artful and HMS Audacious are under construction in an ongoing project that BAE has described as "arguably the most challenging in the UK".

Development has relied heavily on computer-aided design and virtual prototyping, and Astute is one of the first nuclear submarines to be designed entirely in a three-dimensional computer-aided environment.

When it came to assembling such a big vessel, however, there was no way of avoiding the need for space. The Devonshire Dock Hall in Barrow-in-Furness, where the Astute class is being constructed, is the largest shipbuilding construction complex of its kind in Europe, its 51m high hall determined by the need for overhead cranes to clear the vessels' raised masts.

Using a modular approach to construction helped, however. Installing the engine, a task that BAE estimates would have taken two or three days on previous classes, took under five and a half hours.

Rolls-Royce PWR2 nuclear reactor

Powered by a Rolls-Royce PWR2 nuclear reactor, Astute has a submerged speed of around 30 knots and can circumnavigate the entire globe submerged during a single 90-day patrol. In fact, once deployed, Astute is designed not to require refuelling throughout her expected full service life of over 25 years.

The nuclear reactor had to be engineered for an environment where almost 100 people live and work in close proximity, with the submarine commander sleeping less than 10m away from the nuclear core.

The need to be able to work across the wide range of different frequency bands used by other forces around the world means the submarine needs a complex suite of communications equipment. The operating environment is constantly changing with new methods of communication and encryption frequently being introduced by the Royal Navy and allied nations.

Thales 2076 sonar

New secure communications links will provide the improved connectivity essential for operating in conjunction with other task force units, at the same time as monitoring onshore communications traffic.

As well as being one of the Royal Navy's biggest submarines, Astute will be its quietest. Noise and vibration suppression measures such as a cladding of high-density rubber tiles, combined with Thales's 2076 sonar, give it a level of stealth designed to help it identify targets before it is detected. It is the world's most advanced sonar, using bow, flank and towed arrays to deliver 360° coverage.

Moreover, captains won't have to hunch over an optical periscope. Astute is the first Royal Navy submarine not to be fitted with one; instead a range of equipment including thermal imaging cameras and low-light video and CCD TV sensors are used to capture and analyse surface images.

Spearfish torpedo

Astute's six weapons tubes mean her firepower is massively greater than that of her predecessors, and she will be equipped from day one to operate cruise missiles. She will be able to carry 38 torpedoes and missiles - more than any previous RN submarine.

The heavyweight Spearfish torpedo, designed for use against ships and submarines, and the Tomahawk Land Attack Missile capable of carrying out strikes on targets 1,000km inland are discharged through the six torpedo tubes in the bow using a high pressure water launch system. The submarine can also deploy mines.

Air purification

Living space will be a bit more comfortable for Astute's 98 crew and passengers. Unlike earlier submarines, where 'hot bunking' was the norm, everyone has their own bunk. Sanitary fittings comprise five showers, five toilets, two urinals and eight hand basins (the commanding officer has his own hand basin).

The air purification system that lets nuclear submarines remain submerged for so long consists of scrubbers that remove carbon dioxide from the air and pump it into the sea, together with electrolysers to produce oxygen from sea water. Surprisingly, when submariners emerge from a patrol, the 'fresh' air we breathe smells quite foul to them for a time compared with the purified air they have been breathing onboard.

The length of time Astute can remain underwater is limited only by the endurance of the crew and the amount of food that can be carried. During that time, all the food waste and other rubbish has to be stored on-board for eventual disposal on arrival back in harbour. All empty cans, plastic, cardboard and wrappings from the galley are compacted and then placed in special bags in the spaces vacated by the food in the dry stores. Food waste, once put through a macerator, is sent to its own storage tank until it can be disposed of.

Further information

To see the Astute submarine cutaway diagram in full, download the PDF.

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