The Type T-51b (No.11) was a remodelling effort aimed at meeting the weight expectations of its predecessor, the Type T-51a (No.10), which failed to meet its targets. Efforts were made to reduce weight and simplify construction by eliminating the fluid coupling and employing a four-shaft propulsion system. The number of torpedoes was reduced to two, while the 25 mm guns were increased to three. Despite these measures, the weight was only reduced to 75 tons which together with slow production was on path to fail like the previous T-51a. Harassment of shipping lanes by US patrol boats prompted the emergency development of the next Type B (Otsu/乙) small patrol boat (Type T-38) with higher production output. Consequently, further orders for the Type T-51 were cancelled, with only 7 completed (No.11-17), 3 scrapped (No.18-20), and an additional 20 planned (No.21-41) also cancelled.

It was originally introduced as the Type T-51 in Update 1.89 "Imperial Navy", modeled as a T-51a with a triple mount 25 mm in the rear, but was remodeled in Update "Drone Age". Compared to the Type T-51a, the T-51b has more conventional gun placement and angles, and it offers only 2 torpedoes. The T-51b can be played aggressively due to well-positioned autocannons, decent survivability, and small hitboxes for guns and gunners. It easily out-damages most boats at its BR and lower. However, it struggles against high-caliber, armor-piercing shells and has poor anti-air capabilities, requiring smart positioning to avoid dive-bombers. Its good manoeuvrability helps in dodging torpedoes.