The Collaborative International Dictionary of English v.0.48:

Marching \March"ing\,
   a. & n., fr. March, v.
   [1913 Webster]

   Marching money (Mil.), the additional pay of officer or
      soldier when his regiment is marching.

   In marching order (Mil.), equipped for a march.

   Marching regiment. (Mil.)
   (a) A regiment in active service.
   (b) In England, a regiment liable to be ordered into other
       quarters, at home or abroad; a regiment of the line.
       [1913 Webster]