Britain's entire fleet of attack submarines is currently out of operation due to repair and maintenance work, it has been reported.
Seven nuclear-powered vessels, including three new Astute class submarines, which cost more than £1 billion each, and four Trafalgar class boats are all currently classed as non-operational, according to the Sun.
The UK's Vanguard submarines, which carry Trident nuclear missiles, are in operation but according to the newspaper it is the first time in decades the Royal Navy has no attack submarines ready.
Five of the submarines are having refits or maintenance after breaking down, while HMS Ambush has been recalled to Britain for repairs after colliding with a merchant vessel in Gibraltar.
The remaining attack submarine, HMS Astute is having trials at sea following maintenance work, and is weeks away from being operational for missions, according to the report.
A Royal Navy spokesman said: "We don't comment on specific submarine operations.
"Britain has a world-class fleet, the Royal Navy continues to meet all of its operational tasking, deploying globally on operations and protecting our national interests as Britain steps up around the world."
The Astute class vessels are the most powerful attack submarines ever operated by the Royal Navy.
They weigh around 7,400 tonnes, equivalent to nearly 1,000 double-decker buses, and are 328ft (100m) long.
Armed with Tomahawk cruise missiles, the Barrow-built vessels can accurately strike targets up to 1,200 miles (1,931km) from the coast.
Advanced stealth technology means they can remain undetected despite being 50% larger than the Trafalgar class submarines they will replace.
Their nuclear reactors will not need refuelling in their entire 25-year life and they make their own air and water, enabling them to circumnavigate the globe without needing to surface.
The news follows last month's revelation that a test firing of a Trident missile by the Royal Navy off the coast of America last June failed.