By the Mexican-American War in 1845, the US Army uniform featured another set of changes. Soldiers began wearing roundabouts, which were primarily made of blue wool. Additionally, the pants would feature vertical stripes and chevrons on their sleeves in yellow that would mark their ranks. The Army also replaced tombstone caps with forage folding caps. Uniforms worn by the Regular Army of the United States during the Mexican War were based on regulations adopted in 1832 when the uniform was completely redesigned. Facing colors worn on the uniform of America's armies from the Revolutionary War were restored, Mexican-American War uniform those being: buff for generals and staff; white for infantry; and red for artillery.

Three uniform sets were authorized: a dress uniform; a winter fatigue uniform; and a summer fatigue uniform. The winter uniform was worn by all ranks during the Mexican War, although some officers and units wore the dress uniform. Officer's rank was denoted on shoulder straps of the fatigue uniform, and on epaulets of the dress uniform. All officer shoulder straps were bordered in gold except for the infantry who wore shoulder straps with silver borders. Non-commissioned officers wore chevrons on their fatigue jackets.