Like a military operation, the project to test how traffic might flow around southeast England in the event of a no-deal Brexit started before dawn. And like many a military operation, it ran into trouble soon after making contact with reality.

The Department for Transport had asked for between 100 and 150 trucks to assemble Monday morning at a disused airfield in Kent. In the event, 89 turned up.

Those that were there queued on the runway, waiting to be moved. In 2015, the pro-Brexit U.K. Independence Party proposed reopening Manston Airport, to help the local economy. This was probably not what they meant.

For the rest of the morning, the vehicles moved in convoys back and forth to the port of Dover in tests that Britain’s Road Haulage Association said were too limited in scope to replicate the chaotic scenes that could play out if traffic is held up by customs delays after March 29.

“This should have been done nine months ago,” RHA policy director Duncan Buchanan said in an interview. “Preparation needs to be phased, needs to be thought through, dealing with thousands of lorries and, very important, dealing with the behavior of individual drivers.”

The exercise is designed to test the U.K.’s readiness in case Prime Minister Theresa May fails to get her Brexit deal through Parliament and the country crashes out of the bloc without an agreement to smooth the split.

The impact on the transport system — especially goods movements across the U.K. border — would be potentially huge. Trucks are currently carried between Dover and Calais, 25 miles away across the English Channel, with minimal delay. But customs checks, if required, could take up to 45 minutes per vehicle, risking road backups as long as 17 miles.

The exercise, known as Operation Brock, is turning the Manston Airport site into a mass holding bay for heavy goods trucks. That’s intended to provide an alternative to Operation Stack, in which trucks are parked on part of the M20 motorway, amid concern that the transport artery could become irretrievably congested in the event of significant delays at the border.

“We do not want or expect a no-deal scenario and continue to work hard to deliver a deal with the EU,” the Department for Transport said in a statement. “However, it is the duty of a responsible Government to continue to prepare for all eventualities and contingencies, including a possible no deal.”