Up to 1,000 defence workers could be redeployed to help the government cope with a no-deal Brexit, according to a memo seen by the BBC.
The message, sent to staff in the Defence Equipment and Support agency, appeals for volunteers.
The note said it was “uncertain” what work would be required if the UK leaves the EU without an agreement.
But it said redeployment in these circumstances would offer a “real development opportunity”.
The SNP said Brexit was causing “chaos and uncertainty”, but the government said the civil service had the “flexibility to deliver”.
Liberal Democrats Brexit spokesman Tom Brake accused the Conservative party of “scaremongering about a no-deal Brexit when the prime minister could easily take the option off the table”.
He called for another referendum, adding: “Theresa May is attempting to run down the clock, tinker with unviable solutions to the Irish border and frighten MPs, businesses and the public into supporting her already defeated deal.”
Defence Equipment and Support is the agency within the Ministry of Defence that supplies the Army, Royal Navy and RAF with everything from food to fighter jets.
It employs almost 12,000 civil servants and military personnel at 150 bases across the UK and abroad.
The memo, issued by senior manager Neville Parton, said up to 1,000 staff might be needed for redeployment.
He said the agency had been asked to identify volunteers “across all levels and role profiles” as part of contingency planning for a no-deal Brexit.
Mr Parton said defence workers could be needed to support other government departments and local government.
“This provides a real development opportunity to take on a fresh challenge – developing new skills and experience,” he wrote.
“It’s currently uncertain what type of support might be required, for how long and where people might be required”.
The memo suggested any redeployment should not last for not more than six months.
The deadline for applications was 25 January – nine weeks before the UK’s scheduled departure from the EU on 29 March.
The SNP’s foreign affairs spokesman, Stephen Gethins, said “the chaos and uncertainty is all-consuming”.
He added: “The government wants to divert 1,000 officials away from vital work supporting our armed forces, without the slightest clue what they’re going to be doing.
“The UK government’s contingency planning for a no deal is the very definition of too little, too late”.
‘Departments share staff’
The redeployment request appears to be part of wider government efforts to prepare for Brexit and a possible no-deal scenario.
There have already been reports of staff from the departments for education and international development shifting to the Department for Environment, Food and Rural Affairs to help with farming and fisheries.
There will be much work to do in these areas when the UK pulls out of the EU’s common fisheries and agriculture policies.
A government spokesperson said: “The civil service has the flexibility to deliver government priorities and deploy resource appropriately to do this.
“This includes departments sharing staff and working together on joint projects”.