Development:
The development for this vehicle began in 1943 to supplement the firepower the T-34 and KV-1 has. Before then, the T-34 and KV-1 tanks are more than adequate to deal with the German Panzer forces, but by the end of 1942, the appearance of the Tiger I revealed that the German armoured forces were becoming more developed and more armoured. This reveal showed the Red Army that needed better guns in order to deal with the rising threat of these new German vehicles.
The search for a better gun led to the development of the D-5 85 mm gun, which was a modified anti-aircraft gun made by design bureaus of Vasiliy Grabin and Fyodor Petrov. It was found that the new gun was unable to be mounted on the current T-34 or KV-1, so it was to be mounted as a self-propelled gun like the SU-122, which is a self-propelled gun made on a T-34 chassis. The vehicle to be produced was designated the SU-85 and was similar to the SU-122, just replacing the 122 mm gun with an 85 mm one. The gun that was to be mounted in the self-propelled configuration was designated the D-5S (S for self-propelled) and the vehicle was produced at the Uralmash factory. Modifications were made overtime during its production such as a telescopic sight and a new ball gun mantlet, these modified vehicles were designated the “SU-85-II”. Up to 2,050 units were produced from mid-1943 to late 1944.
Combat usage:
The SU-85 saw service in August 1943 in Soviet service, which coincides the time the Soviets engage in a counteroffensive against the Battle of Kursk. It was praised for its low profile to be able to conceal itself and its excellent mobility. The initial production batch had low visibility due to lack of optics, with only four periscopes in the design, but this was improved on the SU-85M with a commander’s cupola seen on the later variants of the T-34. The 85 mm gun was able to destroy a Tiger tank from 1000 meters out, proving much capable against the newer German tank designs. Though capable, its firepower was still seen as lacking considering the Tiger could still destroy it and T-34s from up to 2,000 meters away. The lack of range on the SU-85, plus the up-arming of T-34s from the 76.2 mm F-34 gun to the same 85 mm gun as well in the T-34-85 caused the production of the SU-85 to be cancelled in late 1944 as it no longer provided any beneficial firepower over the standard tank unit.
Even after it was retired from Soviet service, replaced by the more powerful SU-100, it was exported to Soviet allies in the Warsaw Pact after World War II. The SU-85s were either kept as tank destroyers or converted into armour recovery or command vehicles. These vehicles saw service in North Korea, Vietnam, and may still be in service today by Central European countries like Albania, Bulgaria, Yugoslavia, and Romania.
The increasing armour thickness of the enemy’s new heavy tanks necessitated a more powerful SPG. A newly planned 100 mm weapon was being reworked. So in July 1944, the 85 mm D-5-S85 cannon was installed in a newly designed SPG cabin with thicker 75 mm frontal armour, a spacious fighting compartment and a command cupola. This SPG was designated SU-85M and was produced until December 1944. The vehicle, equipped with a new gun mantlet, fired at a rate of 6-8 shots per minute. Its elevation angle was -5° to +25°, and its traversing angle was 20° (up to 10° to each side). In contrast to the SU-85, the vehicle’s ammunition capacity was increased to 60 shells. The SPG’s crew used PPSh submachine guns and F-1 hand grenades for self-defence.
In 1944, 315 SU-85M SPGs were manufactured in total.
The SPGs were used as cover for medium tanks and to offer them fire support when necessary. They were able to quickly move around the front both defensively and offensively. In defence, SU-85s often made use of ambush tactics. The vehicles hid at convenient distances along the enemy tanks’ path and, letting them approach to within 300-600 m, opened precision fire. Before T-34-85 tanks went into mass production, this SPG was the primary means of effective battle against German tanks and played the important role of a mobile tank destroyer in the Red Army.
Captured SPGs of this type were used by the Wehrmacht. There were entire regiments of tank destroyers consisting of these vehicles – the 23rd Tank Division, for example.
SU-85 and SU-85M SPGs were put into service in the Polish Army.
In spite of all the SPG’s advantages, its firepower was insufficient to combat enemy heavy tanks at long ranges.