On the afternoon of July 2 at Gettysburg, Captain Bigelow withdrew his 6 Napoleons "by prolonge." How exactly was this done? Descriptions in histories are vague - even Bigelow's own account. I know how the prolonge is attached and that the cannon is fired and pulled back on the recoil, but how was each cannon withdrawn to the next firing position? By manpower? Attached to the limbers?