During the end of World War II, in order not to consume too many resources to produce a new aircraft, engineers began trying to make small modifications to produce specialized aircraft. There were several new variants, in particular the development of the G.55 which was modified to create the G.56 variant and also the G.55S variant. The G.55S was a variant specifically for attacking enemy ships (S standing for Silurante; "torpedo"). It could mount a torpedo in comparison to the standard G.55. Only a few examples were built and used in battle but did not find any success against ships, being more used as an air superiority fighter.

The G.55S was introduced in Update 1.69 "Regia Aeronautica" as a pre-order premium pack prior to the update that also allowed access into the Italian Closed Beta Test. It was discontinued from the store after the 2019 Summer Sale, but was later reintroduced for War Thunder's 7th Anniversary as a premium purchasable in-game for Golden Eagles. The G.55S is a torpedo fighter, it is a very good plane because of its manoeuvrability and endurance which allows it to perform turn fight and energy fight manoeuvres. The plane can have a torpedo or a set of two 50 kg or 100 kg bombs useful for CAS in realistic battles. The plane is quite resistant to damage caused by enemy aircraft and anti-aircraft. When the G.55S is not being used as a torpedo fighter, it is best used as a low to medium altitude (2-5 km) fighter. With three MG 151/20 autocannons, it will make short work of all fighters and, with careful aiming, can be used to effectively destroy heavy fighters and even the heaviest of bombers. When attacking heavily defended targets (such as B-17 bombers), approaching from the rear, where the enemy has most defensive turret coverage, is not recommended. Fiat G.55 series aircraft (in general) do not have much armour. The armour is only comprised of a 50 mm bulletproof windshield and an 8 mm armoured steel seat. There are no armoured headrests or floor plates to offer increased pilot protection from bullets coming from underneath or behind the plane.