HMS Achilles (S125)

For other ships with the same name, see HMS Achilles.

HMS Achilles (also known as Astute Boat 7) is an Astute-class nuclear-powered fleet submarine under construction for the Royal Navy and the seventh in her class. The boat has had its name changed twice, having previously held the in-work name of Ajax and Agincourt.^[10][11]

HMS Ambush, another Astute-class submarine, during sea trials off the coast of Scotland
History
United Kingdom
Name	HMS Achilles
Builder	BAE Systems Submarine Solutions
Cost	£1.640B (budget)[1]
Laid down	14 May 2018[2]
In service	Projected 2028/early 2029[3][4]
Identification	Pennant number: S125
Status	Under construction[5]
General characteristics
Class & type	Astute-class fleet submarine
Displacement	Surfaced: 7,000 to 7,400 t (6,900 to 7,300 long tons; 7,700 to 8,200 short tons)[6][7] Submerged: 7,400 to 7,800 t (7,300 to 7,700 long tons; 8,200 to 8,600 short tons)[6][7]
Length	97 m (318 ft 3 in)[6][7]
Beam	11.3 m (37 ft 1 in)[6][7]
Draught	10 m (32 ft 10 in)[6][7]
Propulsion	Rolls-Royce PWR 2 reactor, MTU 600 kilowatt diesel generators
Speed	30 kn (56 km/h; 35 mph), submerged[6][7]
Range	Unlimited[8]
Endurance	90 days[8]
Test depth	Over 300 m (980 ft)
Complement	98 (capacity for 109)[6]
Sensors & processing systems	Thales Sonar 2076 Atlas DESO 25 echosounder 2 × Thales CM010 optronic masts Raytheon Successor IFF
Armament	6 × 21 in (533 mm) torpedo tubes with stowage for up to 38 weapons:[9] Tomahawk Block IV cruise missiles Spearfish heavyweight torpedoes

The confirmation for the seventh and final Astute-class boat was given in the Strategic Defence and Security Review 2010, although the order was not placed until 2018.^[12]

On 11 December 2012 the British government announced that long-lead items had been ordered for boats 6 and 7.^[13]

On 6 March 2018 the Defence Procurement minister Guto Bebb confirmed that the MoD had gained Treasury approval to sign a contract for Astute Boat 7,^[14] after a leaked Navy document had suggested it might not be procured as a cost-saving measure.^[15] In May 2018 it was reported that construction of Boat Seven had begun.^[16] She had been projected as being ready for service by early 2026, to be based at Faslane (HMNB Clyde).^[2][17][4] However, it was subsequently reported that her in-service date slipped substantially and she is now likely to commission in 2028 or early 2029.^[18][19]

Design

Propulsion

Achilles' PWR2 nuclear reactor will not need to be refuelled during the boat's 25-year service. Since the submarine can replenish her air supply and purify water underway and while submerged, she will be able to circumnavigate the planet without resurfacing. The submarine's main limitation will be from the three months supply of food carried for the 98 officers and ratings.

Weapons

Achilles will have provision for up-to 38 weapons in six 21-inch (533 mm) torpedo tubes.^[20] The submarine will be capable of using Tomahawk Block IV land-attack missiles with a range of 1,000 miles (1,600 kilometres)^[21] and Spearfish heavyweight torpedoes.

Name

Originally the vessel had the in-work name HMS Ajax, and then HMS Agincourt. In January 2025, the government announced she would be named HMS Achilles. It was reported that the name change had been requested by the King.^[22]