Soviet armored doctrine was wholly rewritten during World War 2 (1939-1945) following the German invasion of the Soviet Union through "Operation Barbarossa". A large focus was eventually placed upon mobile artillery support that involved rocket fire ("Katyusha" systems) with towed artillery elements and, beyond that, Self-Propelled Gun (SPG) units. This wartime experience considerably influenced designs that would appear after the war which saw "big-gunned" vehicles become the norm in supporting major offensives. The 2S7 "Pion" (Peony") was taken into inventory in 1976 and its design was centered around a massive 203mm gun barrel which sat atop a tracked chassis. Despite its Cold War roots, this effective fire support vehicle remains in service to this day (2015).
When recognized by the West, NATO assigned the designation of "M1975" ("Model 1975") to the 2S7. It carried the official Soviet Army designation of "SO-203" as well. When adopted by the service, the 2S7 became the largest Self-Propelled Artillery (SPA) vehicle in service anywhere in the world.
With the arrival of the T-80 Main Battle Tank (MBT), the Soviet Army had an all-modern track-and-wheel chassis from which to spawn a line of associated vehicles from. The 2S7 was developed to support offensive actions involving tanks as well as infantry and other mobile assets for frontline service involving indirect fire. The 2S7 became a 46.5-ton vehicle mating the 203mm 2A44 series howitzer atop the T-80 tank chassis which utilized a V-46-I V-12 turbocharged diesel-fueled engine of 840 horsepower and was fitted at the middle of the hull. The vehicle component retained its torsion bar suspension system for off-road travel and could reach speeds of 31 miles per hour with an operational road range out to 400 miles. Overall length was 10.5 meters with a width of 3.38 meters and a height of 3 meters. Armor protection was for only the crew held in the hull (in a forward-mounted cab sporting roof hatches) and measured 10mm in maximum thickness.
The standard operating crew numbered fourteen (seven were carried on the primary vehicle with the remainder brought along in an assist vehicle) though only the driving and command positions located at the front cabin were wholly protected. This meant that the gunnery grew was completely exposed at the rear-top of the hull and also at the mercy of the elements and nuclear/biological/chemical warfare.
The 203mm 2A44 gun system, with its integrated mounting and recoil hardware, was sat over the rear of the hull. This weapon provided engagement ranges out to 37.5 kilometers and supported the use of Rocket-Assisted Projectiles (RAPs) which drastically increased ranges out to 47 kilometers giving the vehicle a hefty "punch" for indirect fire service. The mounting hardware allowed an inherent traversal of 15-degrees to the right or left before the entire vehicle needed to be turned into the direction of desired fire. Its elevation span was from 0 to +60 degrees. Prior to firing, a large spade located at the rear of the hull was lowered to brace the vehicle for the impact of recoil forces to follow. A load-assist mechanism aided in the reloading process involving the large shells and associated propellant charge components. 203mm projectile reloads were managed by an accompanying ammunition carrier/reload vehicle commonly fielded with such units. The 2S7 gun carrier section stowed four ready-to-fire 203mm projectiles on its hull.
The 2S7 designation marked original production models of 1976 and minor improvements produced the 2S7N mark in the following years. The 2S7M "Malka" was introduced during 1983 as a modernized variant with updated Fire Control System (FCS), improved rate-of-fire (up to 2.5 rounds-per-minute), and increased onboard storage of the 203mm rounds (from four to eight). The BTM-4 mark was an off-shoot design of the 2S7 and outfitted with trench-digging equipment to serve in the support role to 2S7 detachments.
The 2S7 was eventually taken into the inventories of several Soviet allies and supported states including Angola, Azerbaijan, Belarus, Czechoslovakia, Georgia, Poland, Slovakia (limited number), Ukraine, and Uzbekistan. Former Soviet examples were absorbed into the new Russian Army after the fall of the Soviet Empire whilst others found in former states were reconstituted by local armies. Czechoslovakia utilized the vehicle series from 1984 to 1994 after which examples were sold off to Angola. Polish examples were retired in 2006.
Due to the need for big guns in the ongoing War in Donbass (2014-Present) between Ukraine and Russia, Ukrainian stocks of 2S7 systems - once laying in reserve/storage - were refurbished for active service once more. Ukraine has managed a stock of some 99 2S7 vehicles at one point.