Only one of the Royal Navy’s Type 45 destroyers is operational, ministers have admitted.
HMS Defender, recently at the centre of a diplomatic row with Russia following a voyage off the Crimean peninsula, is the only vessel of the class without an issue.
The other five Type 45s all need work, either planned or due to problems developed while at sea.
Commons Defence Committee chairman Tobias Ellwood suggested the situation was “operationally unacceptable”.
Both Defender and HMS Diamond were part of the carrier strike group (CSG), the UK’s attempt to demonstrate its naval power around the world.
But Defence Procurement Minister Jeremy Quin said HMS Diamond had experienced “some technical issues” and was having maintenance, inspection and “defect rectification”.
HMS Daring and HMS Duncan are having planned “deep maintenance”, while HMS Dauntless has been upgraded and is due to return to sea for trials this year.
HMS Dragon is undergoing “planned maintenance” in advance of further operational commitments.
Mr Quin told MPs on the committee: “We have two Type 45s embarked with the CSG, Diamond has got current issues but I hope they will be able to be rectified shortly.”
Mr Ellwood said: “HMS Defender is now our only current operational Type 45.
“If that ship experiences propulsion problems as we have seen across the Type 45 family, then our carrier group would have to be forced to lean on a Nato ally to ensure that we have destroyer protection.
“That really indicates – bottom line – we need a bigger navy.”