Origin of expression 'at the double'

Me maw used to say to me 'at the double', meaning for me to come as quick as possible. Just wondering today: what was the origin of this saying? It seems to me that the words don't apply to anything really specifically, so can some one provide a feasible explanation?

Solution 1:

Just two points Ham and Bacon didn't make clear: double time (the command is "At the double" in the British Army and "On the double" in the American) is literally twice the speed of a normal march, so 72 paces a minute (Britsih Light Infantry pace and I believe also the norm in the USMC) becomes 144, which is pretty much a run. And it's not 'would give the command': the practice continues, and probably will as long as armed forces remain in being, so it's 'gives' or maybe 'will give'.