2B1 Oka, (Russian: "2Б1 Ока" - "Oka River"), is a Soviet 420 mm (17 in) self-propelled heavy mortar. 2B1 is its GRAU designation. It was designed to deliver tactical nuclear payloads, however it was plagued by technical issues caused by the sheer size of the gun and the massive recoil during firing. With the advances in tactical ballistic missile technology, development of the Oka was cancelled in 1960 before it could enter service.