LONDON — HMS Artful, the third of seven new nuclear attack submarines destined for the Royal Navy, has started sea trials, the boat's builder, BAE Systems Submarines, said on Aug 13.

The Astute-class submarine emerged from the dock at BAE’s Barrow-in-Furniess yard for its first sea trials ahead of joining sister boats Astute and Ambush, already in service with the Royal Navy. Subject to the outcome of the sea trials, the Artful, which cost more than £1 billion (US $1.56 billion), is expected to be commissioned around the end of the year.

Armed with Tomahawk land attack missiles and Spearfish torpedoes, the 7,400-tonne Astute-class subs are replacing Swiftsure- and Trafalgar-class boats in Royal Navy service. The four remaining boats in the expected seven-strong fleet are in various stages of construction.

HMS Audacious is the next submarine set to be completed at the BAE yard, which is also gearing up to build Britain's next generation of ballistic missile submarines, with the first metal cut planned for 2016. BAE expects to launch Audacious in the fourth quarter of 2016 and the submarine is scheduled to exit the yard the following year.

The sea trials of Artful follow the report by the government's  Major Project Authority (MPA) that it had issued an amber/red warning following higher than expected on spending on the Astute program. Such a An amber/red warning defines a program as requiring urgent action to avert the program being derailmented.   

 BAE and the Ministry of Defence have already responded to the shortcomings with a number of improvement initiatives aimed at addressing the major risks.

 A Ministry of Defence spokesperson said: "Submarine build programmes are extremely complex and significant steps have been taken to address the issues raised by the MPA," an MoD spokesperson said. "The Astute programme is progressing to deliver world-class submarines with the third, of seven, planned to enter service with the Royal Navy towards the end of the year."

The government set up the Major Project Authority was set up by the Government in 2011 to scrutinisze progress on major capital programs across all departments. It reported in June that spending on the Astute program for 2014 was £87.5 million higher than the planned £558 million. 

The build program, which early in the contract suffered cost overruns and delays, remains on schedule

Responding to a report in a national newspaper today pointing up the overspend, BAE defended the program.

It said in a statement: "To design and build a nuclear-powered submarine is one of the most complex engineering projects in the world, and BAE Systems works closely with the MoD to develop a sustainable submarine enterprise."

"Artful set sail today to begin sea trials having been launched in a significantly better, more mature, material state than her predecessors. This is the third of seven highly capable submarines delivered to the Royal Navy, and the improvements made on Artful will be embedded on the remaining submarines in the class," it said.