Complex sentence: Even when nominally "resting" a trooper's time was never his own--horse-pickets still had to do their turn every night, guards, pumping parties for watering the horse and endless other working parties had to be supplied.
Split into simpler sentences: Even when nominally "resting" a trooper's time was never his own. Horse-pickets still had to do their turn every night, guards, pumping parties for watering the horse and endless other working parties had to be supplied.