The passage of a river in the presence of an enemy, whether acting offensively or in retreat, is an operation of great delicacy and danger.  In either case the army is called upon to show the coolest and most determined courage, for its success will depend on its maintaining the strictest discipline and good order.

In the case of a retreat the bridge should be covered by field intrenchments, called a tete de pont, and defended by a strong guard.  If the river be of moderate width, the enemy may be kept at a distance by heavy batteries on the opposite shore.  As soon as the passage is effected by the main body, the bridge, if permanent, will be blown up, or otherwise destroyed by the miners, and if floating, will be swung round to the other shore.  The rear-guard will pass over in rowboats, or the end pontons detached for that purpose.  An army retreating in the face of an enemy should never rely upon one single bridge, no matter what may be its character:  for the slightest accident happening to it might expose the whole army to inevitable destruction.

The passage of a river by main force, against an enterprising and active enemy on the opposite shore, is always an operation of the greatest difficulty, and not unfrequently accompanied with the most bloody results.

The most effectual method of accomplishing this object is by stratagem.  Demonstrations are made at several points at the same time:  bodies of troops are thrown across, after nightfall, in rowboats or by flying-bridges, to get possession of the opposite bank.  The vanguard of light cavalry may cross by swimming.  The pontoniers should have their bridge equipage in readiness near the intended point of passage, so that it can be thrown across with the greatest possible rapidity, while the advanced guards are still able to keep the enemy at a distance.  Under favorable circumstances the pontoniers will have the bridge in readiness for the passage of the army before the enemy can collect his troops upon the threatened point.

Cannon-balls and hollow shot are the most effectual means for destroying an enemy’s bridge when our batteries can be planted within reach.  When this cannot be done, we must resort to fire-boats, floating rafts, &c., to accomplish our object.  Operations of this kind carried on in the night, are most likely to succeed.

To protect bridges from the action of these floating bodies, stockades, or floating chevaux-de-frise are constructed across the stream at some distance above the bridge; strong cables, or chains stretched directly across the river, or with an angle up stream, may be used in place of stockades, or in conjunction with them.  Guards should be stationed above the bridge, with boats, ropes, grapnels, &c., for the purpose of arresting all floating bodies and drawing thorn ashore, or directing them safely through the draw in the bridge arrangement.

The troops especially charged with the construction and management of the various kinds of military bridges, are denominated pontoniers.  The duties of these troops are arduous and important, and, in a country like ours, intersected by numerous water-courses, the success of a campaign will often depend upon their skill and efficiency.