The Royal Navy's largest warship, which only recently underwent a £65m refit, is to be scrapped.
It comes after the Prime Minister announced the 2015 Strategic Defence and Security Review on Monday.
No mention was made of HMS Ocean during that address to the House of Commons, although Conservative Lord Earl Howe spoke about her decommissioning during the House of Lords debate on the defence review.
The Royal Navy flagship, currently deployed on Operation Cougar 15, will now be removed from service in 2018.
Ocean launches assaults from the sea and played a key role in Afghanistan and Libya
Maria Eagle, Labour's Shadow Defence Secretary, told The Huffington Post UK the decision was "a hammer blow" for the Navy at a time when no like-for-like replacement is due.
The Queen Elizabeth-class aircraft carriers, which are touted to take the place of Ocean, will not be in service before 2020. Ms Eagle said:
"In 2010 the Tories scrapped the Navy's flagship, HMS Ark Royal. Now we learn they will shelve our current flagship, HMS Ocean.
"The Government needs to come clean and explain exactly why it is retiring this key capability not only months after it was re-fitted, but years before the new class of aircraft carriers will be ready for service.
"With serious manpower issues unresolved, questions about the number of warships, and years more without maritime patrol capabilities, it is becoming clear this defence review is a real hammer blow for the Royal Navy."
It comes after an already tough defence review for the Senior Service. Already struggling with recruitment in certain areas, it wanted 2,000 extra sailors to man the two Queen Elizabeth-class aircraft carriers currently under construction. It'll get 400.
The Royal Navy will also only get eight Type 26 Frigates, instead of the 13 originally planned. The government say this is enough to provide adequate protection for the Queen Elizabeth-class carriers.
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This will allow for the building of up to five of a new lighter, cheaper, class of general purpose frigate, along with freeing up money for the additional 400 Royal Navy personnel. Ms Eagle continued:
“This Defence Review will not undo the damage to our Armed Forces caused by the last one, when the Government reduced the UK’s Defence budget by 14.1 per cent over the course of the Parliament.
“The Ministry of Defence has lurched from crisis to crisis under David Cameron’s watch. This is a Government which, since coming to office, has left the UK with aircraft carriers without aircraft, without maritime patrol, and with plummeting morale in our Armed Forces. We will therefore judge the government by its actions rather than its words."
“In an increasingly dangerous world, the UK needs a proper, joined-up strategy to place our Defence and Security on a sustainable footing. Instead the Tories have created huge capability gaps, which our Armed Forces are still living with.”
An MOD spokesman, meanwhile, said:
“HMS Ocean will not decommission early and will continue in service as planned well into this Parliament. As part of the SDSR process, the decision was taken not to extend her and to decommission her in 2018, in line with her 20 year life span.”