The Defence Secretary has rejected reported suggestions that defence insiders thought the British Army's most sophisticated armoured vehicle would be "useless" against anything more than "incompetent enemies".
It comes after claims in The Times that there were delays due to issues with the Ajax's gun, including the integration of the cannon with a specially-built turret, and a shortage of funds.
Sir Michael Fallon denied that the £3.5 billion programme to build the vehicles could be delayed due to the alleged glitches with the weapons system, however.
He also told the Commons Defence Committee work on integrating the weapons system for the Ajax armoured vehicles was running on time and on budget. He said: "We don't agree with the article that appeared in The Times this morning.
"The Ajax is designed to protect itself to a degree that it is scalable to the threat that it faces. These are not tanks and they're not going to be used as tanks, and you shouldn't expect them to have the armour that tanks do."
"We believe Ajax is the best in class and the use of manoeuvre, and well-practised drills, for example, should reduce the threat of direct artillery fire.
"I would also just add, in respect to the article this morning, that the qualification of the weapons system and the integration of the weapon into these vehicles is running on schedule at the moment and it is running to budget."
American company General Dynamics has been developing the vehicles for a number of years, and in 2015 was awarded a £3.5 billion Ministry of Defence contract to deliver 589.
Work on building the first Ajax vehicles will begin next year and the 40mph machines will become the first fully-digital armoured fighting vehicle in UK military history.
They will be built at a disused forklift truck factory in Merthyr Tydfil, South Wales, which will be transformed into a specialist engineering hub.
Forces TV's Carla Prater visited General Dynamics' plant in Wales in September last year for an exclusive first look - click below to watch.
The first of the 589 vehicles - which come in six "variants" - is expected to be completed in 2018.
The first Army units will then receive the vehicle by mid-2019 and they will be ready to deploy from the end of 2020.
Click below to watch the Ajax's first live fire test...
Officials say the new plant will create 250 jobs as well as support another 2,800 posts across the UK.
Controversy arose in 2014, however, after then-Prime Minister David Cameron claimed 1,300 jobs across the UK would be assured by the deal.
But according to the Daily Mirror, it later emerged that 40% of the work would be done by overseas firms, meaning Britain would lose £1.4bn. A Ministry of Defence spokesperson said at the time:
"We are assembling these vehicles in South Wales, supporting thousands of UK jobs and ensuring our servicemen and women have the very best equipment."