Engineer troops attached to an army are habitually employed in supervising the construction of forts or field works of a nature more permanent than the lines need by the troops in motion, and in repairing roads and making bridges.  I had several regiments of this kind that were most useful, but as a rule we used the infantry, or employed parties of freedmen, who worked on the trenches at night while the soldiers slept, and these in turn rested by day.  Habitually the repair of the railroad and its bridges was committed to hired laborers, like the English navies, under the supervision of Colonel W. W. Wright, a railroad-engineer, who was in the military service at the time, and his successful labors were frequently referred to in the official reports of the campaign.

For the passage of rivers, each army corps had a pontoon-train with a detachment of engineers, and, on reaching a river, the leading infantry division was charged with the labor of putting it down.  Generally the single pontoon-train could provide for nine hundred feet of bridge, which sufficed; but when the rivers were very wide two such trains would be brought together, or the single train was supplemented by a trestle-bridge, or bridges made on crib-work, out of timber found near the place.  The pontoons in general use were skeleton frames, made with a hinge, so as to fold back and constitute a wagon-body.  In this same wagon were carried the cotton canvas cover, the anchor and chains, and a due proportion of the balks, cheeses, and lashings.  All the troops became very familiar with their mechanism and use, and we were rarely delayed by reason of a river, however broad.  I saw, recently, in Aldershot, England, a very complete pontoon-train; the boats were sheathed with wood and felt, made very light; but I think these were more liable to chafing and damage in rough handling than were our less expensive and rougher boats.  On the whole, I would prefer the skeleton frame and canvas cover to any style of pontoon that I have ever seen.

In relation to guards, pickets, and vedettes, I doubt if any discoveries or improvements were made during our war, or in any of the modern wars in Europe.  These precautions vary with the nature of the country and the situation of each army.  When advancing or retreating in line of battle, the usual skirmish-line constitutes the picket-line, and may have “reserves,” but usually the main line of battle constitutes the reserve; and in this connection I will state that the recent innovation introduced into the new infantry tactics by General Upton is admirable, for by it each regiment, brigade, and division deployed, sends forward as “skirmishers” the one man of each set of fours, to cover its own front, and these can be recalled or reenforced at pleasure by the bugle-signal.

For flank-guards and rear-guards, one or more companies should be detached under their own officers, instead of making up the guard by detailing men from the several companies.