The 2S7 Pion ('Peony') was the largest-caliber self-propelled artillery system in widespread service with USSR, which at 203-mm was on par with the US's heaviest artillery. Like most Soviet SPGs, it features an all-welded steel hull and has a promient crew compartment located at the front of the vehicle, with both driver and commander given windscreens with armored shutters, roof hatches, and a single day periscope. The engine compartment is located behind, after which is another crew compartment at the rear of the vehicle. The 2S7's main armament is a massive 203-mm L/56.2 gun which noticeably lacks a fume extractor or muzzle brake. The gun can fire a range of conventional amunitions up to a range of 37.5 km or 47.5 km with rocket-propelled projectiles up to a rate of two rounds per minute thanks to an ammunition handling system. It can also fire concrete-piercing, nuclear, and chemical munitions, and NBC protection is also included. Stability is provided by a large recoil spade in the rear, hydraulic shock-absorbers, and the ability to lower the rear chassis, ovearll the Pion prepare a fire mission in 5-6 minutes. The Pion saw action for the first time in Afghanistan and later in the two Chechen wars, and have been used by both Russia and Ukraine during the ongoing war. It was exported to numerous Warsaw Pact allies as well as Soviet successor states.

The 2S7 (Obyekt 216) began development in 1967 with various different calibers under initial consideration before settling on 203-mm, which also resulted in the designation SO-203. It entered service in 1975 and was given a NATO designation of M1975 that same year. An upgraded version is known as the 2S7M which features improved fire control to achieve a rate of fire of 1.5-2.5 rounds per minute.