Retiring by prolong was a method of firing the gun while retiring. The limber and team was turned so that the prolong rope could be hooked from the Lunette ring on the gun to the pintle hook on the limber. The number three man rode on the axle of the gun reclining to the breech and stopped the vent and carried the vent pick in his mouth. [rather nasty to do] The rest of the crew maintained their relative positions at the gun, marching beside it as it was withdrawn, and loading the piece as it moved. When the command "ready" was given, the horses were stopped, the gun was aimed, number four inserted the primer, and number three hopped off the axle.
When the gun was fired, number three hopped on the axle and the team moved on without further command, and the process repeated.

The horses had to move at the walk so that the crew could complete the loading process. It is a bit awkward for the drill due to the moving gun. It is a rough job for the number three man as he has his right arm around the tube to hold on and must thumb the vent and prick the cartridge with his left hand. We do this for demonstrations, and generally the gun is going to move between 30 and 50 yards between shots.

Hope this helped