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The Koizumi KS9K Kyusen is a single seat carrier based fighter, manufactured by the Koizumi Aircraft Company and operated by the Empire of Japan from 1941 to 1948. The KS9K was officially designated as the A7K or the Type 1 Carrier-based Fighter (一式艦上戦闘機 ichi-shiki-kanjō-sentōki). 

Design and Development

Name

In the Koizumi designation "KS9K", "KS" refers to Kanjō Sentōki, which means its a carrier-based fighter, "9" meant it was the ninth model of the carrier based fighter series, and "K" indicated the manufacturer, Koizumi.

The A7K fighters were designed to use their speed to take down and evade enemy fighters, in contrast to the A6M.

Operational history

The A7K entered service in the early 1941. They were first supplied to the 4 Kōkūtai who were stationed in Manchuria. They performed great against Soviet aircraft. Their initial armaments however proved to be ineffective against heavier planes, prompting Koizumi to redesign the fighter to include heavier guns Despite being a naval fighter, the Yōtei-class carriers and Shimosa were the only carriers carrying the A7K fighters.

Variants

KS9K (A7K)

The inital produced variant of the Kyusen fighter, it had an armament of six 7.7 mm machine guns.

KS9K2 (A7K2)

The most common variant of the A7K fighters. Original A7K fighters were converted into A7K2 during their service. The armaments of the A7K2 are two 12.7 mm machine guns and two 20 mm cannons.

KS9K2 Umikaze (A7K2M1)

The Dive Bomber variant of the KS9K2. This variant of Kyusen was used extensively by the 10th Fleet  as their primary dive bomber.

KS9K3 (A7K3)

The enhanced fighter variant of the Kyusen Series. Unlike the previous Kyusens, the A7K3 had a modified A4 engine and four 20mm cannons. These planes were rushed into combat and was quickly supplied to the 4 Kōkūtai