The Pacific Squadron was part of the United States Navy squadron stationed in the Pacific Ocean in the 19th and early 20th centuries. Initially with no United States ports in the Pacific, they operated out of storeships which provided naval supplies and purchased food and obtained water from local ports of call in the Hawaiian Islands and towns on the Pacific Coast. Throughout the history of the Pacific Squadron, American ships fought against several enemies. Over one-half of the United States Navy would be sent to join the Pacific Squadron during the Mexican–American War. During the American Civil War, the squadron was reduced in size when its vessels were reassigned to Atlantic duty. When the Civil War was over, the squadron was reinforced again until being disbanded just after the turn of the 20th century.

The California Battalion was formed during the Mexican–American War (1846–1848) in present-day California, United States. It was led by U.S. Army Brevet Lieutenant Colonel John C. Frémont and composed of his cartographers, scouts and hunters and the California Volunteer Militia formed after the Bear Flag Revolt. The battalion's formation was officially authorized by Commodore Robert F. Stockton, commanding officer of the U.S. Navy Pacific Squadron.