Flooding worries for Royal Navy's new multi-billion pound submarine HMS Astute

The Royal Navy's new multi billion pound hunter-killer submarine HMS Astute encountered a flooding problem during sea trials, the Ministry of Defence has revealed (PA)

The Royal Navy's new multi billion pound hunter-killer submarine HMS Astute encountered a flooding problem during sea trials, the Ministry of Defence has revealed.

Officials said the multibillion pound nuclear-powered attack vessel was forced to resurface after it let in tens of litres of water during testing last year.

Electrical switchboards were also found to be fitted incorrectly, while concerns emerged about the accuracy of nuclear reactor monitoring instruments.

Despite the teething problems, defence officials said the issues had been rectified and that it was "normal for first of class trials to identify areas where modifications are required".

Referring to the flooding incident, which was caused after a metal cap, believed to be on a cooling pipe, corroded, a Ministry of Defence (MoD) spokesman said: "During trials last year HMS Astute experienced a leak which was immediately isolated and the submarine returned safely to the surface.

"An investigation found one small part which had not been made of the correct material had corroded.

"A replacement was fitted at sea and the submarine continued with her programme.

"BAE Systems has carried out a full assessment which concluded all similar parts were fitted correctly."

The spokesman added that electrical switchboards on board Astute, which ran aground near Skye off the west coast of Scotland in 2010, had not been fitted to Naval Engineering Standards and have since been reinstalled.

Concerns that nuclear reactor monitoring instruments were giving inaccurate readings because the wrong type of lead used in certain components were also raised during the trials.

The MoD said a full assessment concluded the material had no effect on the accuracy of any readings and no impact on the submarine's operation.

Responding to corrosion problems, which were identified on Astute and the second Astute class submarine HMS Ambush, the spokesman added: "All Royal Navy submarines are subject to a continuous, thorough assessment of their components to minimise the risk of corrosion."

Officials would not comment on reports that Astute also suffered also suffered from speed and propulsion issues during the trials.

The MoD added: "HMS Astute's sea trials were designed to rigorously test all aspects of the submarine to meet the exacting standards required for operations.

"It is normal for first of class trials to identify areas where modifications are required and these are then incorporated into later vessels of the class.

"These will be the most technologically advanced submarines ever to serve with the Royal Navy and will provide an outstanding capability for decades to come."

The Astute Class of attack submarines are the most technologically advanced in the Royal Navy and will progressively replace the Trafalgar Class currently in service.

HMS Astute which was built by BAE systems, is yet to start formal service.

PA