If the chests be not water-tight and are at the usual height of two feet and ten inches above the ground, a ford deeper than two feet four inches cannot be crossed without danger of wetting the ammunition.
If the chests be water-tight or means have been taken to raise them high enough, a depth of 3⅓ feet may be safely attempted.
When the ford is deeper than this, the cannoneers must carry over the cartridges, fuzes, and primers in the pouches, which they hold above the water. The chests are sometimes removed and taken over in boats. In crossing streams that cannot be forded, when there are no bridges, the horses are swum, and the carriages and harness crossed on rafts, etc.
PASSAGE OF MILITARY BRIDGES.
At the entrance of the bridge the lead-and swing-drivers dismount and lead their pairs. A distance of 12 yards is taken between the carriages, and the gait is free and decided; the drivers keep the carriages as near the middle of the floor as possible. If the flooring be wet, battens should be nailed across it to keep the horses from falling. If the bridge begins to rock, the passage of the column is suspended.
In passing over a flying bridge all the drivers dismount and hold their horses; the lead-and swing-horses should be taken out and led onto the bridge or boat; the brakes should be applied to the rear, so that the carriage cannot be run back.
PASSAGE ON ICE.
Ice 3 or 4 inches thick will bear infantry.
Ice 4½ inches thick will bear light guns or cavalry.
Ice 6 inches thick will bear heavy field-guns.