S-23 180mm field gun
At the beginning of the 1950s, the Soviet Army wanted to equip itself with a family of large caliber long-range guns. Although several models of 180, 203, 210 and 280mm were designed, only the 180mm piece would go into service. In 1955 a huge 180mm towed gun was seen for the first time with designation “180 mm gun S-23“, which raised expectation and concern in Western media, which at first and for almost 20 years took it for a 203mm caliber gun.
S-23 field gun gallery and more info