rafts, or by "conversion," as referred to in the books, and as practiced by the regular engines officers while attached to this brigade, as well as by others, was uniformly by successive pontoons, thereby reducing the time of construction but in a limited degree, and never beyond half of that of the usual method by successive pontoons.
The process is simply to have the wagon bridge trains brought into such position, well closed up, as to be unloaded simultaneously along the shore, as in most cases can be done, and as is the most natural and expeditious method, with ample force of men, and then, with small bridge squads previously detailed, to lay the several bays of the bridge along the shore, also simultaneously, while the abutments on the shore ar eat the same time being constructed by other squads, when the bridge or long raft, to fill the space between the abutments, can be swung with the oars, aided by the current or wing, into the desired position, and made complete in a very few minutes by connecting the ends of this raft with these abutments.
This method of laying pontoon bridges had occurred to me, and I had directed it to be practiced with the canvas pontoon train at Beufort, S. C., in May, 1862, and again I proposed it to the officers of this brigade in April of this year, soon after receiving this command. But though I continually described and urged it upon the officers, the want of opportunities for trial while in front of the enemy, and the persistent adherence to the old methods by these officers when the bridges were then laid or removed, with my indisposition to force the new methods in such positions, had delayed the successful practice of it until we reached this depot camp in July of this year. And though this plan was then ordered and minutely described to the officers for their practice here-being designedly left to them for the first three or four weeks-the continued disbelief in it, or the quiet opposition which I was afterward assured had existed with about all the officers of the brigade, was so great that no advance or improvement appeared; in fact, I had the written report of the drills here describing the building of bridges of some 300 feet in forty-five to fifty minutes by the old method of successive pontoons, while the new method was reported as requiring one and a quarter hours.
This satisfied me, then, that my instructions had either been mis-understood or had not been zealously carried out, and I at once took the personal direction of the drills, and at the first trial the bridge of 300 feet was completed in twenty minutes; at the next, after due preparation of the necessary material, the bridge to span the Eastern Branch here, fully 1,300 feet long, was laid complete, swing into position, and connected in half an hour, and in the next three or four drills this time was reduced to twenty minutes or less for the complete construction, swinging around, and connecting of the bridge ready for the passage of artillery.
The detail of time (which I think is now reduced to nearly its minimum) for the several parts of the work, I may mention is very nearly, for squads of 6 to 7 men of some experience, about seven to nine minutes for constructing the bridge or raft along the shore, about seven to nine minutes to swing the bridge to, between the abutments, and about two to three minutes to connect and complete the whole, or some eighteen to twenty minutes in all. The time for swinging the bridge will, of course, vary with the width of the river, currents, wind, &c., while the time for the construction of the raft along the shore and its connection to the abutments will be about the same for any length of bridge.