Source : Webster's Revised Unabridged Dictionary (1913)

Prolonge \Pro*longe"\, n. [F. See {Prolong}.] (Field Artillery)
   A rope with a hook and a toggle, sometimes used to drag a gun
   carriage or to lash it to the limber, and for various other
   purposes.

Source : WordNet®

prolonge
     n : a rope fitted with a hook and used for towing a gun carriage