A young army officer's wartime diary recounts departure from the military academy and follows marches, sieges, and engagements through a campaign in Mexico. It pairs immediate battlefield observation, sketches, and manuscript facsimiles with candid notes on camp life, logistics, and the uneven discipline of volunteer troops. The entries describe landscapes and towns encountered, assess fellow officers, and register youthful impressions that contrast with the author’s later reputation. The volume provides practical detail about engineering and military routine alongside reflective commentary on leadership, morale, and the limitations of relying on volunteer forces.