On July 24,1853, the Manco , a gunpowder storeship in San Francisco Bay, caught fire suddenly and threatened a blast that might devastate the crowded wharf. Desperate fire fighters soaked the Manco and the neighboring Canonicus with water while a fleet of small boats supported the heavy hoses. Amazingly, they prevented any serious explosions. Though they hadn’t actually been witnesses, the genre painters Charles and Arthur Nahl re-created the scene three years later, basing their colorful docudrama on a delivery boy’s sketch.