But as it sailed into Portsmouth harbour at 8am on Wednesday, this gun-grey military transport was set for a radical makeover, as Portsmouth firm Burgess Marine prepared to transform it into one of the UK's largest high-speed passenger ferries.

The Incat 050 catamaran had been built in Hobart, Tasmania, in 1998, and was chartered to the American military since 2001, before being returned to Australia 18 months ago.

The ship is now moored at Portsmouth docks in readiness for months of intensive engineering works by Burgess, who will turn its helicopter landing pad into a sky lounge, gut and refit its interior and restructure the 96-metre aluminium catamaran frame to add a stern-loading vehicle ramp.

Burgess Marine director Nicholas Warren said she has had quite a journey.

He said: 'She was successfully delivered from Hobart in Australia. That's an 11,000 mile journey, a long way to come to get to Pompey. We're gearing the business up now to be focussed on the project over the next five months.

'I think she has been on active service with the navy, and I think done some time in the Gulf. But she started as a passenger ferry, and is now going back to her roots.'

The deal will net Burgess around £3m, and up to 100 workers are expected to be involved in the completion of the project.

Mr Warren said that because the ferries were aluminium, much of the work more resembled aircraft construction than traditional shipbuilding – requiring a set of specialist skills specific to Portsmouth.

He said: 'This is very, very significant for us, because we've been working all over the world, sending staff to carry out work everywhere from Jeddah to Canada, but a refit of this size on an aluminium fast ferry hasn't been done in the UK before.

'It's good news for the ship building industry in Portsmouth as well, because it shows we've got the skill set to carry out this kind of work.'