Spiralling costs of the Type 45 destroyers were criticised by the House of Commons defence committee as early as 2009. The Royal Navy had originally requested 12 ships but the cost of the advanced ships meant the force ended up with just six.
The ships are powered by integrated electric propulsion, using very high-voltage electrics. Warships with electrical failures may be unable to navigate, with the destroyers drifting at sea until power is restored, and weapons systems may be unable to function.
At least one new generator is expected to be needed on each ship, requiring a major refit of a vessel where space is already at a premium.
The work will be furthered hampered by a shortage of marine engineers, which has led to the Royal Navy being forced to recruit from the US Coast Guard. Last year it was estimated that the Royal Navy was short of about 500 engineers, despite also recruiting many from Canada and other Commonwealth nations.