What is the Pion artillery weapon used in Ukraine?

What is the 2S7 Pion (M-1975) artillery weapon being used in the Ukrainian conflict?

The tracked heavy gun is used by both sides and has a range of 37.5km.

Weighing 46.5 tonnes, it is the size of a large house.

• Royal Marines deployed to guard British Embassy in Ukraine, reports suggest
• UK would run out of ammunition 'in two weeks' in a war against Russia
• Abandon 'arrogant' troop cuts in light of Ukraine war, MOD told

Entering service with the Russian Army in 1975, it destroys stronghold positions by firing 203mm rounds.