Military planners have been assigned to key government departments as officials try to avoid problems in the event of a no-deal Brexit.
Staff have been deployed to plan "for a range of contingency scenarios", according to the Ministry of Defence.
Their role is understood to be exercise planning and overall command and control duties.
The move is believed to be in response to fears of major backlogs, involving lorries and goods at ports such as Dover, if there is no longer frictionless trade with EU nations.
Defence minister Tobias Ellwood told Forces News: "Absolutely it's right for us... to contingency plan.
"This is what we do - we have to work out all sorts of scenarios that might hit Britain," Mr Ellwood said.
"The support that we provide, the military assistance to civil authorities, is something that we do on a daily basis.
"Whether it's for flooding, or whether it's for any form of support that might be required, and that includes a no-deal scenario."
Transport Secretary Chris Grayling told Sky News on Sunday that he talks to Defence Secretary Gavin Williamson "quite regularly" about no-deal Brexit planning.
But he said he does not have the military "actively involved" in no-deal planning beyond the secondment of a "small number" of staff from the Ministry of Defence.
Mr Grayling also said: "I have not asked for military support for the operations in Kent - that will be handled by Highways England and Kent Police."