The Mosquito FB Mk XVIII, also known as the Tsetse, was a special anti-submarine variant of the de Havilland Mosquito. Developed from the FB Mk VI variant, the Tsetse's main differences were its armament, replacing the set of Hispano autocannons with a single 57 mm Molins anti-tank cannon with a 25-round autoloader to strafe enemy U-boats, as well as reinforced armour plating to protect the underside of the aircraft. Due to its specialised role, only 18 Mk XVIIIs were produced. Despite the small production run, the Tsetse proved to be a success when it first entered service in 1944; it was credited with sinking several German U-boats and surface vessels using its large autocannon, and it would serve until the end of hostilities in Europe.

Introduced in Update 1.39, the Mosquito FB Mk XVIII is a specialised variant of the Mosquito armed with a large 57 mm autocannon. Although the plane was designed for the anti-submarine role, it can also be used against enemy tanks with great efficiency. The 57 mm gun offers a powerful AP shell with high penetration values, allowing the Tsetse to pierce enemy armour with ease. However, due to its specialised design, the Tsetse is ill-equipped against aerial threats: the 57 mm gun only has an option for an AP belt that tends to over-penetrate enemy aircraft and is therefore quite ineffective against them, while the other guns are four weak 7.7 mm machine guns. This, along with the Tsetse's reduced agility due to reinforced armour, effectively restricts it to the ground attack role.