The Silent Service makes an Astute purchase

HMS Astute enters Faslane

The Astute Class is Britain’s newest and largest attack submarine

The Royal Navy’s Submarine Service dates back to 1901, when, despite a senior officer calling submarines “Underhand, unfair and damned un-English” six Holland-Class boats were ordered for trials. They were soon followed by the much more advanced A-Class design, and the fleet expanded through the First World War and the inter-war period. When the Second World War began the Royal Navy had 60 modern submarines with nine more under construction; by 1945 it had 160. After the war numbers began to fall, and sometimes the decline has seemed terminal. Shrinking budgets and the rising cost of new equipment have squeezed the Submarine Service relentlessly. In 1960 HMS Dreadnought (S101) was launched, making Britain the third nation to operate nuclear submarines, and the cost increased even more. By 1975 the fleet was down to four nuclear-powered ballistic missile submarines, eight nuclear attack boats and 20 diesel-electric boats. The last diesel-electrics were retired in 1994 and by 2000 there were only four Vanguard-class Trident missile submarines and ten nuclear attack boats, five each of the Swiftsure and Trafalgar classes. Now the attack boat force has been cut even more, to seven. The Swiftsures are gone and the Trafalgars are slated to follow by 2022. For now, though, the plan is to stay with a total of seven boats and that means replacing the Trafalgars with a more advanced design. That design is the Astute-class, and two of them – HMS Astute and HMS Ambush – have already joined the fleet, replacing the last Swiftsures.

HMS Tireless
The T Boats have new sonars and are still capable, but they’re getting older. HMS Tireless will be retired in 2014.

The new A Boats are the largest attack submarines ever built in the UK. They were initially known as the “Batch 2 Trafalgar,” but really there’s no comparison. A Trafalgar displaces 5,300 tons dived; an Astute weights in at 7,400. A lot of this extra size is down to the choice of reactor. To save money the designer, BAE Submarine Solutions, opted to use the Rolls-Royce PWR 2 originally designed for the 15,900 ton Vanguard-Class Trident missile boats. This has a larger diameter than previous attack boat reactors and wouldn’t fit in the much more slender T-Class hull. On the other hand the PWR 2 has a “whole life” core, so it will never need to be refuelled, and it’s reported to be six times as powerful as the PWR 1 fitted to the older boats.

hms astute control room
HMS Astute’s control room may look cramped, but it’s far larger than in older boats.

BAE managed to turn the larger hull diameter to their advantage by maximising the Astute‘s internal space. All previous Royal Navy submarines have used “hot bunking,” where a crewman coming off watch goes to sleep in a bunk just vacated by a member of the previous watch. Now every crewman has his own bed space and doesn’t have to worry about the personal hygiene of anyone else. At the same time improved technology has reduced crew requirements. It takes 130 officers and men to run a Trafalgar; the much larger Astute only needs 98. There are bunks for a total of 109, though, allowing specialists to join the crew if required for a mission.

The PWR 2 reactor itself powers a series of steam turbines, which generate electricity to run the boat’s systems and operate a pump-jet propulsor. This expels a jet of water to drive the boat, and gives off a lot less noise than a conventional propeller. It’s a smaller and more practical version of the caterpillar drive from The Hunt For Red October. The Astutes have a top speed of at least 29 knots, although the first boat has had problems reaching high speed because of a design problem which BAE say they’ve now solved. The hull is coated in over 39,000 anechoic tiles to absorb reactor and turbine noise as well as incoming active sonar pulses, making the new boats the quietest British submarines ever. If the reactor goes down there is also a bank of 600kW MTU Diesel generators.

Sensors are one of the most vital systems on any attack submarine, and the Astute is state of the art in this department. The sonar system is the 2076, produced by Thales. It includes at least seven separate sonars, configured for collision avoidance, oceanographic monitoring, active and passive search, and fire control. Some journalists have claimed that an Astute patrolling off the British coast could hear a ship leaving New York harbour. That’s probably an exaggeration. On the other hand Royal Navy sources say that it can hear the noise of a bus 60 miles away and it’s almost certain that’s a considerable understatement. BAE themselves say that the 2076 is the best sonar in the world, and as the US Navy admit to being “taken aback” by HMS Astute‘s capabilities on a recent exercise they’re probably not wrong.

As well as sonar the Astutes have an array of other sensors. They can continuously monitor water temperature, and are fitted with two non-penetrating periscopes these Thales CM010 models don’t need to pass through a hole in the pressure hull; the complete mast is mounted inside the sail (which is reinforced for breaking through ice) and images are sent to the control room by fibre-optic cable. The periscope heads have thermal, low-light and colour TV sensors, so they work perfectly well in darkness. There are also an array of communications and electronic warfare masts.

HMS Astute launching a cruise missile
HMS Astute launches a Tomahawk cruise missile. These weapons give her strategic reach.

The Astutes are very good at detecting targets, and once they’ve done so they can also hit them effectively. The standard combat load is 39 weapons. The main weapon for anti-submarine and anti-ship attacks is the Spearfish high speed heavy torpedo, which has a range of at least 30 nautical miles and a top speed that’s classified but probably over 70 knots. The main land attack system is the Tomahawk Block IV cruise missile. It’s unknown what other weapons are certified for the weapon tubes, but Stonefish mines are a likely option. The boats can also carry a dry deck shelter for deploying special forces.

The development of the Astutes has shown up some problems, but this is almost inevitable with a new class of highly sophisticated warship. In total seven of them are planned, with two already in service and four more building. In an ideal world more orders would double the fleet, but if the Royal Navy has to be restricted to only seven boats the Astute, probably the most sophisticated attack submarine in existence, gives the maximum possible capability.