A CONTROLLED evacuation had to be carried out at BAE Systems in Barrow over the weekend.
BAE Systems evacuated workers from Audacious after sensors detected high levels of carbon monoxide.
A spokesperson for BAE Systems said: "At 7.15am, on Saturday, there was a controlled evacuation of Audacious after the submarine's monitoring systems detected higher-than-normal levels of carbon monoxide on-board.
"By early afternoon this was resolved and employees returned to work."
Audacious, the fourth of seven Astute class attack submarines being built for the Royal Navy, was launched by BAE Systems at the end of April.
The 97-metre long, 7,400-tonne nuclear-powered submarine was lowered into the dock water for the first time to begin the next phase of its test and commissioning programme. It is due to leave Barrow for sea trials next year.
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