Kent Resilience Forum made the announcement yesterday saying it was a precaution in response to the reduced ferry capacity at the Port of Dover caused by operator P&O.
Video: Barry Goodwin
From 8pm, last night the motorway closed between Junction 9 for Ashford and Junction 8 for Maidstone to allow it to be deployed and it reopened at 6am this morning with the system in place.
On Thursday, P&O announced 800 staff would be made redundant and employees on board the ships were given just five minutes to get their stuff and leave.
Protests at the port followed on Friday and the government announced the firm could be facing unlimited fines for their actions.
While it believes there is 'sufficient capacity to accommodate displaced P&O freight', Kent Resilience Forum says it chose to activate the measure to minimise disruption across the county.
Operation Brock is designed to keep the motorway moving when services are disrupted across the English Channel.
The Londonbound carriageway is split into a contraflow system by a moveable concrete barrier between Ashford and Maidstone.
HGVs and other freight heading for the Port of Dover or Eurotunnel will use the coastbound carriageway where it will be queued if necessary.
All other traffic – including local freight and car drivers headed for the continent – should follow the signs and cross over to enter the contraflow on the London-bound carriageway.
The barrier is deployed using two specialist machines, and over 14,000 tonnes of concrete blocks were moved into place in just a few hours, together with more than 8,000 cones.