The Collaborative International Dictionary of English v.0.48:

Double-quick \Dou"ble-quick`\, a. (Mil.)
   Of, or performed in, the fastest time or step in marching,
   next to the run; as, a double-quick step or march.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Double-quick \Dou"ble-quick`\, n.
   Double-quick time, step, or march.
   [1913 Webster]

   Note: Double-quick time requires 165 steps, each 33 inches in
         length, to be taken in one minute. The number of steps
         may be increased up to 180 per minute.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Double-quick \Dou"ble-quick`\, v. i. & t. (Mil.)
   To move, or cause to move, in double-quick time.
   [1913 Webster]

WordNet (r) 3.0 (2006):

double-quick
    adj 1: (of a marching cadence) very quick