Aircraft, which had been first deployed in combat during World War I, continued to advance rapidly and became a threat to warships and cities. In 1924, the Sasebo Naval District conducted its first exercises simulating air raids. During these exercises, a temporary anti-aircraft gun emplacement was installed atop Mt. Yumihari, which overlooks the naval district. This battery was subsequently used for training in anti-aircraft combat. Then, when the Second Sino-Japanese War broke out in 1937, anti-aircraft batteries were built at 12 locations including that on Mount Yumihari. Toward the end of World War II, from June 1944, this battery was significantly upgraded with the addition of two Type 98 10-centimeter twin-mount high-angle gun turrets, one Type 4 Model 1 anti-aircraft fire radar unit, and other state-of-the-art equipment. This coincided with the advance of American Army B-29 heavy bombers into mainland China, and it is considered the earliest domestic example of an anti-aircraft battery specifically equipped to counter B-29s. The Mt. Tajima anti-aircraft battery fought fiercely against subsequent air raids, and during the June 29, 1945 air raid on Sasebo, it fired 139 rounds across 14 radar-directed engagements. Today, the radar site, gun emplacements, command post, ammunition storehouse, and other facilities remain in good condition, providing a clear picture of the anti-aircraft battery’s layout at the time.