Ambush Takes the Plunge  
(Source: BAE Systems; issued October 4, 2011)
 
HMS Ambush, the second of six Astute-class nuclear attack submarines on order for the Royal Navy, has made her first dive as she works up for her sea trials. Ambush, the second hunter-killer submarine in the Astute Class, has successfully completed her first dive; an important milestone in readiness for the boat’s departure on sea trials early next year.

The dive, known to engineers as ‘the Trim and Inclining Experiment’, proves the boat’s safety and stability in the water and measures the submarine’s performance at a depth of 16 metres. The maiden dive took place over two days and involved more than 70 people including BAE Systems’ engineers, Ministry of Defence personnel and Royal Navy Ship’s Staff.

Commander Peter Green, Commanding Officer of Ambush, stated: “This is a major milestone for Ambush and shows she is firmly on track to exit Barrow early next year in order to commence her sea trials. Nuclear submarines are some of the most complex machines on earth and therefore to see everything come together in order to dive the boat for the first time is very satisfying. It has been a superb team effort between BAE Systems Submarine Solutions, the Ministry of Defence Submarine Project Team and Ambush Ship’s Company”

The ‘‘Trim and Inclining Experiment’ proves the safety and stability of the submarine and sets the standards of operation for Ambush’s performance. Meticulous measurements are taken at every stage of the dive. These include ‘trim draught’ - gauging how far the boat sits underwater to achieve the correct balance, assessment of the boat’s centre of gravity and the stability of the boat intact and in the event of damage.

The experiment takes place in a dedicated deep area of the dock at Barrow-in-Furness known as the ‘basin’ or ‘dive hole’. A set sequence of preparations is made, including diving the submarine on its main ballast tanks, fine tuning the submarine using her trim and compensation tanks, ‘heeling’ or inclining the submarine and surfacing the boat recording draughts.

Prior to Ambush’s sea trials in 2012 a final major commissioning activity, known as Power Range Testing, will take place towards the end of this year. In this test the full propulsion system is put through its paces for the first time.

BACKGROUND NOTES on Astute-Class SSNs:

-- First-of-class, HMS Astute, was formally handed over to the Royal Navy in November 2010 and is undergoing sea trials.
-- Boat 3, Artful: key equipment and systems have been commissioned in the Devonshire Dock Hall (DDH), most recently the boat’s diesel generators commissioned 18 days ahead of schedule.
-- Boat 4, Audacious: all the pressure hull units are now in the DDH and unit outfit and combination is well under way.
-- Boat 5, Anson: the keel laying ceremony takes places on Thursday 13 October and will be marked by the first unit of the submarine moved out of fabrication and into full construction and outfit in the hall.
-- Boat 6: long lead procurement has begun and first steel cut is due in 2012.