The Ministry of Defence (MoD) is selling the Royal Navy's flagship vessel HMS Ocean to help plug a mammoth financial black hole.
The £84 million sale to the Brazilian navy is due to go ahead next month and Ocean will sail to South America in the summer.
Pressed on the amount of money that would be reinvested from the sale, a MoD spokesman confirmed to the Press Association it expected to yield a £55 million net profit, all of which would be pumped back into naval coffers.
In its report published last month, the National Audit Office said that despite building in a £6 billion contingency, there was an "affordability gap" of at least £4.9 billion in the MoD's equipment programme.
However, if all the risks of cost growth associated with the programme were to materialise the shortfall would rise to £20.8 billion, it said.
Announcing the sale of HMS Ocean, Clive Walker, head of the Defence Equipment Sales Authority which managed the deal, said: "We have a proven track record of supplying surplus defence equipment on a government-to-government basis.
"The successful sale of HMS Ocean to the Brazilian navy will provide a financial return to the UK which will now be reinvested in defence."
Modifications to HMS Ocean will be made by UK companies Babcock and BAE Systems, funded by Brazil, ahead of its transfer, the MoD said.
It is understood the vessel will become a fully operational member of the fleet, rather than being used for display purposes.
HMS Queen Elizabeth will eventually take on the role as the nation's new flagship, and will be able to act as a helicopter carrier once its sea trials have been completed.
The MoD spokesman said HMS Ocean's helicopter-carrying capability would not be lost, with the likes of HMS Bulwark and HMS Albion able to take over those duties.
Johnny Mercer, the Tory MP for Plymouth Moor View and a former Army officer and Afghanistan veteran, said HMS Ocean's sale marked "a sad day".
The amphibious warfare craft was host to Theresa May's first visit on board a Royal Navy ship in December 2016, and five years earlier members of its aviation crew became unlikely internet sensations after their rendition of Mariah Carey's 'All I Want For Christmas Is You' went viral.