In 1927, the Bofors company of Sweden had designed a new 75 mm AA gun which was purchased by the Royal Swedish Navy. This was developed into a mobile anti-aircraft gun with a wheeled carriage, which was exported to the Republic of China, Persia, and Thailand.
Japanese forces captured examples of the Bofors M29 75mm AA gun from the National Revolutionary Army of the Kuomintang government of China, and the Army Technical Bureau was impressed with its performance, which was much superior to the existing Japanese Type 88 75 mm AA Gun. By reverse engineering a close copy was designed and went into production in 1943. However, Japan lacked the raw materials and its industrial infrastructure was too damaged by air raids to follow through with mass production. Only 70 units were completed before the surrender of Japan.
The Type 4 75 mm AA gun had a single piece gun barrel with sliding breech, mounted on a central pedestal. The firing platform was supported by four legs, each of which had adjustable screwed foot for leveling.
Coming into service towards the end of the war, all seventy Type 4s that were operational were retained on the home islands as part of the bolstering of Japan's defenses against Allied air raids and against the perceived threat of Allied invasion.