The following pages were hastily thrown together in the form of lectures, and delivered, during, the past winter, before the Lowell Institute of Boston. They were written without the slightest intention of ever publishing them; but several officers of militia, who heard them delivered, or afterwards read them in manuscript, desire their publication, on the ground of their being useful to a class of officers now likely to be called into military service. It is with this view alone that they are placed in the hands of the printer. No pretension is made to originality in any part of the work; the sole object having been to embody, in a small compass, well established military principles, and to illustrate these by reference to the events of past history, and the opinions and practice of the best generals.