convoy guard

They had just come up with the convoy guard, who heard what he said, and somehow or other -- how, it is as well not to inquire -- several of the great lumbering beasts began to bellow angrily and broke into a trot, which probably being comprehended by the drove in front, they too broke into a trot, which in turn was taken up by the spans in the wagons, and the whole line was in motion.

The Kopje Garrison A Story of the Boer War George Manville Fenn 1870