All of Britain's attack submarines are currently out of action, according to reports.
Maintenance, refit or repair work is currently being carried out on HMS Torbay, Trenchant, Talent, Triumph, Artful and Ambush, according to the Sun.
The newspaper claims, meanwhile, that only one submarine, HMS Astute, is at sea but she is having trials following maintenance and is weeks from missions.
Forces TV's Charlotte Banks asked former defence minister and head of the Royal Navy, Lord West, who has been critical of the service's actions since he stepped down, for his reaction to the reports.
HMS Triumph, Torbay, Talent, and Trenchant are all Trafalgar-class submarines which were first commissioned in 1983 and are due to be decommissioned in 2017, 2019, 2021, and 2022.
They are all reportedly getting refits or maintenance.
More: 'Trident: In Numbers'
The Astute-class subs - Astute, Ambush, and Artful - are newer, but Artful is getting maintenance and Ambush was in need of repair after a collision near Gibraltar.
The Sun claims the information has been kept from the Prime Minister because defence chiefs 'fear her reaction'.
UKIP defence spokesman, Bill Etheridge MEP, said:
"This story underlines two vital points... Firstly, that under-investment in our military capacity has left the cupboard bare - the slightest problem exposes the lack of back-up."
"Secondly, our defence procurement, headed by Tony Douglas, on a salary and bonus package in excess of £500k a year is definitely sub-standard.
"We now have ships that break down in warm water, aircraft carriers with no aircraft and not a single serviceable submarine."
"Quite honestly the man should do the honourable thing and resign. He has failed the troops, failed the taxpayer and failed the country."
For its part, the Royal Navy has released a statement saying:
"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."
Four additional Astute-class subs - Audacious, Anson, Agamemnon, and Ajax - are due to be commissioned in 2018, 2020, 2022, and 2024.
Both the Astute and Trafalgar-class subs are nuclear powered.
Cover image: HMS Ambush at its launch in Barrow-in-Furness.