The ZSU-23-4 Shilka is a Soviet self-propelled anti-aircraft system.
I thought the Shilka was an old piece of Cold War kit, but it turns out that, while it may be old, many countries have developed upgrade packs and are still using it.
The ZSU-23-4 (Zenitnaya Samokhodnaya Ustanovka = “anti-aircraft self-propelled system”, 23mm x 4 guns) was designed in the late 1950s to replace its optically-targeting twin 57mm canon predecessor, the ZSU-57-2, with a modern radar-guided system. It went into service in 1962 and over the years around 6,500 have been built.
Many countries, particularly Warsaw Pact, have operated them and they are still in action today in Syria and the Ukraine, though not for air defence purposes. Just as the famous German 88 AA gun in WW2 was discovered to be a formidable anti-tank gun, the Shilka has turned out to be a lethal infantry support vehicle, particularly for mountain campaigns. It came into its own during the Soviet–Afghan War when it was used against Mujahideen positions high in the mountains – targets too high for the max gun elevation of their tanks and other armoured vehicles.
This particular one, on display at the Yorkshire Air Museum, was captured in Iraq.