The Soukou-Tei No.4 (AB-4), the first production model of the Soukou-Tei series, was introduced in 1933 following the success of the AB-1 'Sakigake' and AB-2 'Kachidoki.' Upgrades included dual 7.7 mm machine guns replacing 6.5 mm ones, the 57 mm Type 97 tank gun replacing the 37 mm Type 11 infantry gun, and more efficient welding for lighter yet equally protective armor. A diesel engine further improved mobility, enabling higher speeds. Compared to its predecessor, the AB-4 boasts better performance, firepower, and mobility but still struggles with limitations in open-sea combat. The 7.7 mm machine guns are effective against lightly armored targets like patrol boats and aircraft but lack range, while the 57 mm gun offers strong damage potential hindered by accuracy and velocity issues, making it challenging to engage fast or distant enemies.