More than 400 officers and staff from Police Scotland are being deployed to help with security at this week's G7 summit in Cornwall.
About 200 officers left in a convoy from the force headquarters in Tulliallan, Fife, on Sunday morning.
The remainder will travel before the three-day summit begins in Carbis Bay on Friday.
Chief Constable Iain Livingstone said the deployment would not affect policing requirements in Scotland.
The G7 summit takes place in from 11 to 13 June, with the leaders of the US, Canada, France, Germany, Italy, the UK and Japan attending.
Security for the meeting is being co-ordinated by Devon and Cornwall Police.
Further contingents from Police Scotland will head south in the coming days.
Chief Constable Iain Livingstone said he had consistently made clear the "great benefits" of close co-operation among UK police forces.
"This has been evident over many years in Scotland - from the policing operation in relation to the Lockerbie bombing, to supporting the Commonwealth Games, and will be seen again later this year during the COP26 summit," he said.
"As the UK's second largest service, it is vital we continue to demonstrate our support in this regard.
"I approved the deployment following careful consideration and it in no way affects Police Scotland's ability to meet the policing requirements of our communities in Scotland."