A pledge of £1 billion for the Ministry of Defence (MOD) will not resolve the hollowing out of Britain's armed forces but is just a mere "drop in the ocean" compared to what is needed, a former head of the Royal Navy has said.
Chancellor Philip Hammond announced the move - which he said will boost cyber capabilities, anti-submarine warfare capacity and maintain the pace of the Dreadnought nuclear submarine programme.
The extra funding has been hailed as a "significant win" for Defence Secretary Gavin Williamson, who is said to have "lobbied hard" during his first year in the job.
But Labour peer Admiral Lord West said that the cash - although welcome - "will not stop the hollowing out" of Britain's armed forces.
Delighted that the pledge will mean the Dreadnought programme moves forward, he added: "It doesn't resolve the problem that we have of hollowing out - which is a real problem.
"That is why frigates aren't at sea, the army and the tanks are a mess, and exercises are being affected... it doesn't really address all the other problems within defence."
The cash boost comes amid calls to increase spending to above 3% of GDP on top of a black hole in the MOD budget of at least £20 billion over the next decade.
Lord West agreed the extra funding is just a fraction of what is needed, and that the hollowing out will have to be addressed in the spending review next year.
He said that if more cash does not come then, it means there is a "real, real problem for UK defence".
In March, another £800 million was pledged to defence - £600 million of which was earmarked to help fund four new Trident nuclear submarines - bringing the total to £1.8 billion.
Having previously clashed with Mr Williamson over military spending, Mr Hammond told the Commons as he delivered the Autumn Budget on Monday that as a former defence secretary he understands the immediate pressures.
Former defence secretary Sir Michael Fallon said the extra cash is a "welcome step in a long-running campaign to readjust the Dreadnought budget in particular".
Asked whether it is enough, he said: "No, I would like to see the Government adopt a new higher target now of 2.5% of GDP on defence by the end of Parliament.
"The threats have multiplied in the last year or so... and the budget needs to be increased accordingly."
Labour MP for Plymouth, Sutton and Devonport Luke Pollard said the £1 billion pledge is a "drop in the ocean compared to what the MOD actually needs".
"But I think what our armed forces are looking for is clarity on capabilities - especially because so many have had grey clouds hanging over them for in some cases over a year on whether they will be scrapped," he said.
"I don't think £1 billion, although welcome, gives a reprieve to the Army units, the Royal Navy ships or the aircraft that we know are under threat from MOD cuts."
Welcoming the move, Mr Williamson said the extra £1 billion - which will cover the MOD for the rest of this year and next - "represents a substantial boost".
He said the move "reaffirms our commitment to protecting national security", and will allow the delivery of the existing plans set out within the 2015 Strategic Defence Review.