The USS San Diego on 28 January 1915 while serving as flagship of the Pacific Fleet. Her name had been changed from the California on 1 September of the previous year. On 21 January 1915 the San Diego suffered a boiler explosion. While taking the half hour readings of the steam pressure at every boiler, Ensign Robert Webester Cary Jr. had just read the steam and air pressure on number 2 boiler. He had just stepped through the electric watertight door into number 1 fire room when the boilers in number 2 fire room exploded. In fire room number 2 at the time was Second Class Fireman Telesforo Trinidad, of the Philippines and R. E. Daly, along with one other man. Ensign Cary stopped and held open the watertight doors which were being closed electrically from the bridge, and yelling to the men in No. 2 fire room to escape through these doors, which 3 of them did do. Ensign Cary held the doors open for a full minute with the escaping steam from the ruptured boilers around him. For His extraordinary heroism Ensign Cary was awarded the Congressional Medal of Honor2,3. He would later retire with the rank of Rear Admiral. Fireman Telesforo Trinidad was driven out fire room No. 2 by the explosion, but at once returned and picked up R. E. Daly, Fireman Second Class, whom he saw injured, and proceeded to bring him out. While coming into No. 4 fire room, Trinidad was just in time to catch the explosion in No. 3 fire room, but without consideration of his own safety, passed Daly on and then assisted in rescuing another injured man from No. 3 fire room. Trinidad was himself burned about the face by the blast from the explosion in No. 3 fire room. For his extraordinary heroism Fireman Second Class Trinidad was awarded the Congressional Medal of Honor also for this incident. The San Diego returned to duty as flagship through 12 February 1917, when she went into reserve status until the opening of World War I. Placed in full commission 7 April, the cruiser operated as flagship for Commander, Patrol Force Pacific Fleet .