Defence bosses have already spent at least £381 million overhauling British tanks, new figures reveal, amid concerns over costs and delays.
Lockheed Martin was hired six years ago to overhaul and fit new gun turrets to Britain's ageing fleet of Warriors, which have served in the Gulf, Bosnia and Iraq.
But Ministry of Defence documents forecast the Warrior upgrade is a year behind schedule, with the programme incurring extra costs as a result of delays.
Up to 380 new Warriors were to be upgraded under the original plans, forming the backbone of two armoured infantry brigades planned as part of a reorganisation of the army.
However, The Times reported last month that one of these brigades could be disbanded, with hundreds of its fighting vehicles scrapped as part of a drive to cut costs.
A review of the defence spending programme is also under way, which has led to speculation over cuts to the Royal Marines and the navy's amphibious assault vehicles as well as the Warrior programme.
Labour's Kevan Jones, a former defence minister, said: "Minsters need to urgently explain how £381 million has already been spent on a vehicle that might now only be deployed in very limited numbers.
"The Government's attempts to balance the books of the defence budget are becoming increasingly chaotic."
The £381 million bill for Lockheed Martin's Warrior programme represents the costs to the end of July and was confirmed following a Freedom of Information request by the Press Association.
It includes the design and development of the project, and preparation of demonstration vehicles for a trials programme.
The response also said the MOD was unable to confirm how that compared with the project's original budget.
The so-called Warrior Capability Sustainment Project (WCSP) is the major part of the armoured infantry 2026 programme.
The MOD's major projects portfolio data, published this summer, puts the overall cost of the armoured infantry programme at £1.613 billion, which includes some of the expected in-service costs of the Warrior.
But the report says the Warrior upgrade project now has increased forecast costs "as a result of delays in the demonstration phase", with a focus in 2016/17 on stabilising the programme's costs.
The MOD report also downgraded the Warrior's delivery forecast to "amber/red" in light of "a number of challenges".
It said the MOD now forecasts a "12-month slip to equipment delivery", with negotiations with Lockheed Martin key to addressing this.
An MOD spokesman said of the costs incurred so far: "This money has been used to develop state-of-the-art upgrades and demonstration vehicles for the Warrior platform as we look to enhance it for the future and boost the army's capabilities.
"We are contributing to the cross-government review of national security capabilities and looking at how we best spend our rising defence budget to protect our country in the face of intensifying threats, but any discussion of the options is pure speculation."