Britain's new multibillion-pound hunter-killer submarine, HMS Astute, has been beset by design and construction flaws that have raised doubts about its performance and safety.
Astute, costing £9.75 billion (HK$119.7 billion) and the first of the Royal Navy's seven new submarines, has been unable to reach its intended top speed.
It would even be incapable of keeping pace with the Royal Navy's new aircraft carriers, which will be able to travel at more than 30 knots and need the submarines to protect them. One source said the submarine had a "V8 engine with a Morris Minor gearbox".
Other problems that have affected the vessel include flooding during a routine dive that led to Astute performing an emergency surfacing.
The Ministry of Defence confirmed Astute had suffered some "teething problems".
"It is normal for first-of-class trials to identify areas where modifications are required and these are then incorporated into later vessels of the class," a spokesman said.
The ministry said it could not discuss the speed of submarines, but the spokesman said Astute would "provide an outstanding capability for decades to come".
John Large, an independent nuclear safety analyst and specialist engineer, said: "These problems are much more significant than the niggles and glitches expected to arise during working up of a new class of nuclear-powered submarine.
"Particularly disturbing is the apparent mismatch between the nuclear reactor plant and the steam turbine sets, putting the submarine speed below par and making her susceptible in the anti-submarine warfare theatre."
The opposition Labour Party's defence spokesman, Jim Murphy, said ministers "must be clear over the impact of any problems with this essential programme on timing and cost".
Astute, which is four years overdue and £2 billion over budget, has been surrounded by controversy since it was commissioned 15 years ago.
In 2010, it was marooned off northwest Scotland, a calamity that led to its commander being removed from his post. Last year a senior officer was shot dead by a junior member of the crew.
During exercises off the US east coast, a cap on one of the pipes that takes sea water from the back of the submarine to the reactor began to leak. A compartment became flooded, forcing the commander to surface immediately. Although nobody was hurt, it emerged that a cap was made from the wrong metal, even though records said the right metal had been installed.
It is the problems with propulsion which are the most sensitive. The ministry stated Astute would be capable of 29 knots, but sources said it could not do this.
Rather than building a new power plant for Astute, the ministry chose a reactor from the much bigger Vanguard-class Trident submarines. It was linked to a steam turbine system based on the model used in the aged Trafalgar Class attack submarines.