The vessel has replaced Condor 10 which has been in service since 1993
A former peacekeeping ship once used to rescue people from East Timor has set sail on its maiden voyage from Dorset after being converted into a car ferry.
The new ship, called Condor Rapide, is a high-speed catamaran service which will initially sail between Weymouth and the Channel Islands.
The 86-metre (282ft) fastcat set sail earlier and is due back from the islands at about 2030 BST.
The vessel was known as HMAS Jervis Bay and worked with the Australian navy.
It was the first large catamaran to be used in a naval capacity and has replaced the existing Condor 10 which has been in service since 1993.
The new ferry will sail its current route while work to repair the Condor Express is completed.
From 3 June, the ex-navy ship will switch to its "home route" between the Channel Islands and St Malo in France
Brittany Ferries axed its cross-ferry Barfleur ferry service, which had sailed between Poole and Cherbourg for 17 years, in December citing declining passenger numbers.
However the firm has bought a new £75m ferry to increase sailings from Portsmouth to northern Spain.