Plans by the US to build its first heavy icebreaker in more than 40 years are under fire from a government watchdog.

The Coast Guard and Navy intend to invest up to $9.8bn to build and maintain three heavy polar icebreakers for missions in the Arctic and Antarctic.

But even before pen is put to paper for delivery of the first vessel in 2023, the General Accounting Office (GAO), the key federal watchdog agency, has criticised the programme on design, scheduling and cost grounds.