A group of motor industry manufacturers has written to Andy Burnham and his chancellor to ask for help to switch from supplying parts for cars to making kit for the defence sector.
It comes as orders for vehicles made in the UK fall, while the demand for weapons rises.
The companies warned that if the government fails to step in, tens of thousands of manufacturing jobs that are vital for the economy - in peace or wartime - could be lost.
This would impact the country's ability to ramp up weapons production just as ministers are warning of the possibility of conflict with Russia.
David Roberts, chairman of the Coventry-based manufacturing group Evtec and lead author of the letter, told Sky News' Defence Insider app: "History has taught us one thing, that it's factories that win wars, not necessarily the RAF."
In the run-up to the Second World War, a range of manufacturers switched from making civilian products such as cars and started producing weapons, including Spitfires.
The letter, which was also signed by eight other manufacturers and the president of the Confederation of British Metalforming, signalled an element of similar thinking today - though clearly driven as well by the need to diversify to compensate for declining car orders.
"Over the same period in which our automotive volumes have contracted, the country has committed to the largest sustained industrial demand signal in 40 years," said the letter, which has been seen by Sky News.
The manufacturers were referring to a major investment plan to rebuild the armed forces that was published in June and will also require the UK to regrow its defence industrial base.
"That demand needs precisely what sits in our factories: High-integrity castings, five-axis machining, injection moulding, pressings, fasteners, tube and fabrication, surface treatment, metrology and the quality discipline that automotive volume manufacturing beats into a business," the motor industry manufacturers wrote.
"The capacity exists. The people exist. What is missing is the bridge."
That means the journey that needs to be navigated to move from running factories that make car parts to ones that produce parts for weapons.
Securing the right clearances for the aerospace and defence industry takes time and costs money - something that automobile manufacturers lack even though they are aware that their skills would very much be needed by the defence sector.
"No clearing bank lends against an order book that does not yet exist, and the automotive revenue that would otherwise fund the crossing is the very thing that is falling away," according to the letter, which was sent last week.
It highlighted a decision by JLR - formerly Jaguar Land Rover - to shed 4,000 jobs earlier this month as evidence of the slump in automobile demand.
The signatories to the letter, all based in the West Midlands and the North West, called the redundancy announcement "the first visible crack in a supply chain of 183,000 manufacturing jobs, that has no time left to convert into aerospace and defence unless government moves this autumn".
It takes 18 to 36 months to qualify a factory for the aerospace or defence sector because of a different set of protocols, even though all automotive part manufacturers already operate at a high level, according to the letter.
They urged help from the government, including assistance with gaining the right certifications and a reduction in industrial energy costs.
They also recommended setting up a pilot project in the West Midlands to convert firms in the area from being part of the automotive supply chains to the aerospace and defence sector.
"In return we will commit publicly," the letter said.
"We will invest ahead of confirmed demand, retain and retrain rather than release skilled people, take on apprentices against the new capability rather than the old."
The letter ended with a warning: "The re-sourcing of the UK automotive supply chain is happening now, and its consequence is job losses.
"The orders that will fill European aerospace and defence factories for the next decade are being placed now. Britain has roughly one procurement cycle in which to decide whether the parts inside its own aircraft, submarines and armoured vehicles are made by British companies, or bought from someone else's."
A government spokesperson said: "As part of our Modern Industrial Strategy, we are working with industry to develop more resilience in the supply chain. That includes targeted grants, helping to cut the cost of energy, and boosting the competitiveness of aerospace competitions.
"For defence that means bringing together Britain's defence industry, dual tech sectors, and global financial institutions to mobilise private investment into defence programmes. That is on top of the MOD spending an additional £2.5bn with smaller firms every year by May 2028."
(c) Sky News 2026: Motor industry demands Andy Burnham's help in switching to defence supply
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