The Battle of San Bernardino (May 1 to May 10, 1925) was a military engagement within and around the San Bernardino area (including the town of Riverside and smaller communities in the surrounding San Bernardino Valley), which was a major hub for transportation across Southern California. The first part of engagement was the Japanese 24-hour artillery bombardment of the area, and the later aerial campaign against the city of San Bernardino and Riverside. Camp Hangan was damaged severely, with a majority of its aircraft destroyed, and the remainder were later shot down during the initial battle. American engineers blew two bridges crossing the Santa Ana River to kept the Japanese from entering San Bernardino via Riverside for a while, helping protect fleeing civilians toward Barstow and Las Vegas.
The Japanese finally crossed the river, and pushed inland. The last remnant of American resistance occurred on Mt. Rubidoux, in which American resistance bravely defended the hill from the Japanese. The hill was later captured on May 5th. The Japanese then pushed through Riverside, and towards San Bernardino. The last of the American forces surrendered on the 10th, and were sent to a POW camp. The battle cost the Americans 2,000 men against 15,000 Japanese lost during the battle.