Battle of Monterey The so - called Battle of Monterey , at Monterey , California , was waged on July 7 , 1846 , during the Mexican - American War . The United States captured the town unopposed . The action made the ongoing Bear Flag Revolt superfluous . Preliminaries . Prior to the Mexican - American War the Californi o forces had already driven the Mexican appointed Governor Manuel Micheltorena and most of his soldiers from Alta California . The Californio Governor , Pio Pico , with about 100 poorly armed and poorly equipped soldiers , was nominally in charge in Alta California and had consolidated his forces in Pueblo de Los Angeles — the largest city then in California with about 3 , 500 residents . The main forces available to the United States in California were the about 400 - 500 bluejacket sailors and U . S . Marines on board the five ships of the Pacific Squadron there . Speculating that war with Mexico over Texas etc . was very possible , the U . S . Navy had sent several additional naval vessels to the Pacific in 1845 and 1846 to protect U . S . interests there and prevent possible British action . It took about 200 days , on average , for ships to travel the over - trip from the East coast around Cape Horn to get to California . More ships assigned to the Pacific Squadron would continue to arrive from 1846 to 1847 . Hostilities between U . S . and Mexican forces had been underway in Texas since April 1846 resulting in a formal declaration of war on May 13 , 1846 , by the U . S . Congress . On May 17 , 1846 , unofficial word reached the U . S . Navy fleet of four vessels at anchor in the harbor of Mazatlan , Mexico , that hostilities had begun between Mexico and the United States . Commodore ( Rear Admiral ) John D . Sloat , commander of the U . S . Navy ' s Pacific Squadron , dispatched his flagship , the Frigate , and the Sloop to Monterey harbor where they arrived on July 2 , 1846 . They joined the sloop which was already there . There were U . S . fears that the British might try to annex California to satisfy British creditors . The British Pacific Station ' s ships off California were stronger in ships , guns and men . Battle . Hearing word of the Bear Flag Revolt in Sonoma , California and the arrival of the large British 2 , 600 ton , 600 man , man - of - war , flagship under Sir George S . Seymour , outside Monterey Bay , Sloat was finally stirred to action . On July 7 , 1846 — seven weeks after war had been declared , Sloat instructed the captains of the ships of the Pacific Squadron in Monterey Bay to occupy Monterey with their Marines and Navy sailors . The Californio soldiers had already left the town ' s defenses and gone to Los Angeles . They would have had no gunpowder to use in their few cannon s even if they some had stayed . Two hundred twenty five U . S . Navy officers , sailors , and Marines commanded by Captain William Mervine of the U . S . S . Cyane landed unopposed and captured Monterey without incident . They raised the flag of the United States without firing a shot . The only shots fired were a 21 gun salute to the new U . S . flag fired by each of the U . S . Navy ships in the harbor . The British ships observed but took no action . Aftermath . After the occupation of Monterey the rest of the small towns in California surrendered very quickly without a shot being fired . Once it was seen that the U . S . Navy was taking action the Bear Flag Revolt was quickly converted into an annexation as the California Bear Flag was swapped for the U . S . flag . The Bear Flag revolutionaries were soon combined with John C . Frémont ' s 60 man exploratory force to form the U . S . sponsored California Battalion under the command of Frémont . The California Battalion , which varied from 160 to 400 men , drew regular army wages and were used to garrison and maintain order in the towns that had surrendered . This freed Commodore Robert F . Stockton , who had taken over by July 21 , 1846 , Pacific Squadron ' s Marines and sailors to go on to do other activities . Sloat ' s famous declaration , annexing California to the United States , was met with bitterness and anger by some Californios who had a wide variety of opinions on the subject .