The 2S7 Pion ("peony") or Malka is a Soviet self-propelled gun. "2S7" is its GRAU designation.

It was identified for the first time in 1975 in the Soviet army and so was called M-1975 by NATO (the 2S4 Tyulpan also received the M-1975 designation), whereas its official designation is SO-203(2S7). Its design is based on a T-80 chassis carrying an externally mounted 2A44 203 mm gun on the hull rear.

It takes the crew of 7 men 5–6 minutes to come into action and 3–5 minutes to come out of action. It carries 4 203 mm projectiles for immediate use while the remainder is carried by another vehicle and it is capable of firing nuclear ammunition of the same caliber. The gun has a range of 37,500 m but the range can be extended to 55,500 m by using RAPs (Rocket Assisted Projectiles). The Pion has also been the most powerful conventional artillery piece since entering service in 1983. One interesting feature of the Pion is the firing alarm. Because the blast of the weapon firing is so powerful it can physically incapacitate an unprepared soldier or crew member near it from concussive force, the Pion is equipped with an audible firing alarm that emits a series of short warning tones for approximately 5 seconds prior to the charge being fired.

In particle physics, a pion (short for pi meson, denoted with π) is any of three subatomic particles: π0
, π+
, and π−
. Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force.

Pions are mesons with zero spin, and they are composed of first-generation quarks. In the quark model, an up quark and an anti-down quark make up a π+
, whereas a down quark and an anti-up quark make up the π−
, and these are the antiparticles of one another. The uncharged pions are combinations of an up quark with an anti-up quark or a down quark with an anti-down quark, have identical quantum numbers, and hence they are only found in superpositions. The lowest-energy superposition of these is the π0
, which is its own antiparticle. Together, the pions form a triplet of isospin. Each pion has isospin (I = 1) and third-component isospin equal to its charge (I_z = +1, 0 or −1).

The π±
mesons have a mass of 139.6 MeV/c² and a mean lifetime of 2.6×10⁻⁸ s. They decay due to the weak interaction. The primary decay mode of a pion, with probability 0.999877, is a purely leptonic decay into an anti-muon and a muon neutrino: