The Astute Class submarine - the most powerful and largest sub in the Royal Navy explained

The Navy's submarines are longer than 10 London buses and weigh nearly 7,400 tonnes. As HMS Audacious takes its first test dive, we look at the technology inside.

At the end of January, the fourth Astute-class submarine completed its first ever dive at Barrow-in-Furness in Cumbria. The attack submarine that was built by BAE systems for the Royal Navy was fully submerged, and will be ready for sea trials later in the year.

Named HMS Audacious, she joins HMS Astute, HMS Artful and HMS Ambush as one of the billion-pound Astute-class submarines. We take a look at what these boats are capable of doing.

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(Royal Navy)

What does the Astute-class submarine look like?

It’s large. Weighing 7,400 tonnes and at 97 metres long it can take a 100-strong crew aboard. It’s the largest attack submarine in the Royal Navy.

On-board there are facilities for the crew to live and work, and the submarine can manufacture her own oxygen and fresh water from the sea.

There are also no periscopes. Astute Submarines receive their images from fibre-optic cables rather than the traditional mechanical periscope.

Technology on the Astute submarine

The technology aboard each of these class of submarine is the most advanced in the Royal Navy, with there being 50% more firepower than the existing Trafalgar class submarines.

It runs on nuclear technology which means it never needs to be refuelled and can remain submerged as it cruises underneath the surface.

The 38 weapons onboard includes a spearfish heavyweight torpedo and Tomahawk cruise missiles.


(Royal Navy) 

The torpedo weighs nearly two tonnes and can target ships or submarines up to 14 miles away. It tracks the enemy ship by being guided by a copper wire or using its inbuilt sonar to deliver a 660lb explosive charge. The detonation occurs either when it strikes the hull of a submarine or via an acoustic proximity fuse under the target.

The Tomahawk IV is the latest version of the missile which has a range of more than 1,000 miles. It can also send back images of the battlefield to the submarine.

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Developing the Astute submarine

building(BAE Systems)

Each submarine goes through a naming and first-dive process. For HMS Audacious it undertook its trim dive, where an astute class sub submerges for the first time, in January 2018.

This trim dives, where the sub goes 15 metres down, allows the engineers to calculate the submarine’s precise weight and centre of gravity. As well as the 64 people on board, there’s also 16 tonnes of lead on four trollies which are used to test the stability of the craft.

The Telegraph reported in February 2017 that each sub cost £1.2 billion when it was reporting on controversies that have dogged the Astute submarine development.

The newspaper said that the submarines have been hit by technical problems, which the Ministry of Defence denied.

These reports followed The Guardian’s 2012 reports that the Astute submarines were beset by design and construction flaws.

Anson and Agamemnon, submarines five and six, and a yet unnamed seventh sub are all in different stages of development at the Barrow site, according to BAE Systems.

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