The navy is planning to put old weapons onto its new destroyers as it struggles to get them ready, The News can reveal.
The navy is expected to take the Phalanx system from old ships and put it on the Type 45s to beef up their defences.
The news comes as the Ministry of Defence revealed that two months on it still doesn't know what caused the ship's missile system to fail.
Phalanx is a radar-guided gun that protects the ships from attack if the main missile has not worked.
Several other navies with similar ships have a system like Phalanx, and critics say fitting the old ones is a poor compromise.
Portsmouth South MP Mike Hancock, who sits on the Commons defence committee, said: 'The legacy of the awful start to the Type 45 programme is a ship that has several limitations because of cost.
'Other navies have put the Phalanx type system in place as part of the design, but we are looking at adding technology which is two decades old as a bolt on.'
Since November, the navy has been grappling with the problem with its Sea Viper missile - the main defence for the ship - which is holding up getting the Type 45s ready for active service.
It is a far cry from 12 months ago when crowds gathered in Portsmouth to watch the futuristic HMS Daring arrive in her new home.
The 1bn ship, the first of six in the class, was billed by the navy and manufacturer BVT Surface Fleet as the world's most advanced air defence destroyer.
But while the ship has since been on trials the problem of sorting the Sea Viper system has meant the MoD has had to push back Daring's in-service date.
The in-service date is the moment when the MoD take the ship legally from the manufacturers.
MoD planners had wanted to take the ship on - knowing she could be fitted with a working Sea Viper - next month.
But with no progress from the investigation into the firing failure off the south coast of France, a new timetable cannot be set up.
Steve Bush, a former naval officer and editor of Warship World, said: 'The navy has missed the February deadline for taking on Daring and there is no sign yet of any end date.
'There is no great information coming from the MoD about what went wrong with the missile firing and without that the ship is a 1bn patrol vessel.
'It was a policy decision to split the building of the ship and the missile system, but that is now causing problems.
'It will take an extremely long time before both ship and Sea Viper will be on operational deployment because the missile has been fired four times and it has failed twice.
'They have to resolve what is happening with that and then carry out another test firing from a ship.
That is a completely different game to firing from the barge.'
As well as the cost-saving measures with Phalanx and the problems of Sea Viper, the MoD has still to decide what to do about another major feature of the ship.
When the number of ships was cut from 12 to eight and then six, the navy said it would not have such a big impact because of the Cooperative Engagement Capability (CEC) - a computer system which allows one ship to see what others are doing and co-ordinate action.
The contract for that has still not been ordered.
Mr Hancock said: 'The Type 45s have been beset by problems and it is not a credit to our procurement skills.
'As well as Sea Viper we've got situations like having missile launchers which are potentially weaker than the French and Americans, which is not the world-class status that is talked about.'
For the MoD the context for getting the Type 45s in proper service is the National Audit Office report which criticised a 1.5bn project overspend.
An MoD spokeswoman for defence equipment and support in Bristol confirmed that the navy intended to take Phalanx equipment for the Type 45s when older ships were decommissioned.
She said the MoD did not know what date they would take ownership of Daring.
She said: 'Where the equipment is available for the Type 45s it would be the intention to install it.'
'Investigations into the circumstances of the Sea Viper test are still ongoing.'
LATE AND OVER BUDGET
The Royal Navy's new Type 45 destroyers will be at least two years late and 1.5bn over-budget, the government's spending watchdog revealed last year.
The National Audit Office said the procurement programme, initially meant to total 5bn, would eventually cost an estimated 6.5bn.
The MoD originally planned to buy 12 Type 45 destroyers, but that was reduced to eight in 2004 and in 2008 to just six.
The first of the destroyers, HMS Daring - which was launched in 2006 - is without its full communications system and will not get its new principal anti-air missile system (PAAMS) - which can shoot down multiple enemy aircraft or missiles simultaneously - until at least 2011.
The project was effectively launched in April 1999 when the MoD pulled out of the costly Horizon joint project with France and Italy, but kept on with what is now Sea Viper (the Principal Anti-Air Missile System).
Edward Leigh, chairman of the Commons Public Accounts Committee said of the report: 'There is a familiar ring about equipment procurement which begins with over-optimism and ends with costs soaring and significant delays.'
The MoD is struggling to find cash for a system that underpins its claims about the Type 45s' strength.
The department has yet to make a decision about who will supply the Cooperative Engagement Capability (CEC) - the kit that gives the ships a picture of where threats are in a battle.
When the government decided to cut the number of Type 45s from 12 to eight and then six, it justified the move by saying the destroyers would have world-beating technology.
The CEC is vital to helping destroyers defend the new Queen Elizabeth class carriers because it gives them the best level of information about threats in the area.
After several expensive delays the MoD said it was planning to have the system in place by 2014 - in time for the arrival of HMS Queen Elizabeth - but whether it will be British or American built is still unknown.
The timeframe has been branded 'optimistic at best' by defence experts.
Editor of Warship World, Steve Bush, said: 'There was tremendous opposition to cutting the new ships and the reason for justifying it was having CEC in place.
'It's very, very optimistic to say they will have it and have tested it by 2014.'