On this day 13 May 1846, the United States declared war on Mexico.

Friction between the United States and Mexico, aggravated by an ever-increasing American population in the southwest and admission of the Texas Republic into the Union, resulted in war. The Navy's Home and Pacific Squadrons blockaded the enemy's east and west coasts, seized numerous ports, and conducted amphibious operations. From the Gulf of Mexico, Commodore M. C. Perry, with small sidewheel steamers and schooners, fought his way up tortuous rivers to capture Frontera, San Juan Bautista and other enemy strongholds and supply sources. Sailors from the Pacific Squadron under Commodores John Stoat and Robert Stockton landed at Monterey, San Francisco, and San Diego, assuring success in the California campaign. Veracruz, key to ultimate victory on the Gulf, fell before a brilliantly executed amphibious assault planned by Commodore David Conner. Over 12,000 troops were put ashore with their equipment in a single day, and at the request of General Winfield Scott naval gunners and their heavy cannon landed. Joined by guns of the fleet and Army artillery, the naval battery pounded the enemy into submission, and opened the way for the capture of Mexico City.