On navigable streams a part of the bridge resting on one or two bateaux should be so arranged that it can be shipped out of its place, forming a draw for the passage of river-craft.  Indeed, it would be well, even where the river is not navigable, to form a draw for the passage of trees, and other floating bodies, sent down by the enemy against the bridge.

An ordinary bridge-equipage of bateaux, or light pontons, for crossing a river of from three to four hundred yards in width, and of moderate current, will require a train of from sixty to eighty wagons.[46] Under favorable circumstances, and with a well-instructed corps of pontoniers, the bridge may be thrown across the river, and prepared for the passage of an army in a few hours at most.[47] After the troops have passed over, the bridge may be taken up, and replaced on the wagons in from a quarter to half an hour.

[Footnote 46:  The number of wagons in a ponton train will be greatly diminished if it be found that Indian-rubber boats may be used as supports for the bridge.  The engineer department of our army are making experiments to determine this point.]

[Footnote 47:  In 1746, three bridges of bateaux were thrown across the Po, near Placentia, each fifteen hundred feet in length, and entirely completed in eight hours.  In 1757, two bridges of bateaux were thrown across the Rhine, at Wesel, in half an hour; again, in the same year, a third bridge was thrown across this river near Dusseldorf, in six hours.  In 1841, Col.  Birago, of the Austrian army, arrived on the bank of the Weisgerben arm of the Danube, with his bridge-equipage, at a round trot, and immediately began the construction of his bridge, without any previous preparation or examination.  In less than three-quarters of an hour the bridge was completed, and three loaded four-horse wagons passed over on a trot, followed by a column of infantry.]

The following examples will serve to illustrate the use of different kinds of boat-bridges in military operations:—­the passage of the Rhine, in 1702, by Villars; the passage of the Dnieper and the Bog, in 1739, by the Russians; the passage of the Danube, in 1740, by Marshal Saxe; the passage of the Rhine, near Cologne, in 1758, by the Prince of Clermont; the passage of the Rhine, in 1795, by Jourdan; the passage of the Rhine, at Kehl, in 1796, by Moreau; and again the same year, at Weissenthurn, and at Neuwied, by Jourdan; the bridges across the Rhine, at the sieges of Kehl and Huninguen, in 1797; the passage of the Limmat, in 1799, by Massena; the passages of the Mincio, the Adige, the Brenta, the Piava, &c., in 1800; the passages of these rivers again in 1805; the passages of the Narew, in 1807, by the Russians; the several passages of the Danube, in 1809, by the French and Austrian armies; the passages of the Tagus and Douro, in 1810, by the English; the passages of the Niemen, the Dwina, the Moskwa, and the Beresina, in 1812, by the French; and of the great rivers of Germany and France, in 1813 and 1814.