The fourth Astute class submarine, Audacious, which is being built by BAE Systems for the Royal Navy, has completed her first ever dive.

The trim and basin dive took place over two days in Devonshire Dock, at the Company’s site in Barrow-in-Furness last week. The company said in a statement:

“The operation, which saw Audacious submerge fully under water for the first time, tested many of her on-board systems, and proved the safety and stability of the 7,400-tonne, 97 metre-long attack submarine.

Employees from BAE Systems worked alongside Audacious’ crew, including its Commanding Officer, Captain Scott Bower, to complete the test.”

Officially named in December 2016 and launched in April last year, Audacious is scheduled to leave Barrow for sea trials later this year.

HMS Astute, HMS Artful and HMS Ambush are already in-service with the Royal Navy. Boats 5 and 6, Anson and Agamemnon, along with a seventh, as yet unnamed but likely to be Ajax, Astute-class submarine are in different stages of construction at the Barrow site.

Long lead items for her construction were ordered in 2006 although the actual order was not placed until 2007. Launch was expected in the fourth quarter of 2016, and the submarine was due to leave the yard in 2017. She was eventually formally named in December 2016 and floated out in April 2017, she is due to leave in 2018 for sea trials.

The original budget was £1,279m but by 2015 this had risen to £1,492m.