Battle of Kursk guns and mortars. In 1943 an offensive by the Soviet Central, Bryansk and Western Fronts against Army Group Centre was abandoned shortly after it began in early March, when the southern flank of the Central Front was threatened by Army Group South. Soviet intelligence received information about German troop concentrations spotted at Orel and Kharkov, as well as details of an intended German offensive in the Kursk sector through the Lucy spy ring in Switzerland. The Soviets verified the intelligence via their spy in Britain, John Cairncross, at the Government Code and Cypher School at Bletchley Park, who clandestinely forwarded
Battle of Kursk amid poor weather and with the German forces exhausted and in need of refitting, the offensives of Operational Order No. 5 were postponed. On 15 April, Hitler issued Operational Order No. 6, which called for the Kursk offensive operation, codenamed "Zitadelle" ("Citadel"), to begin on 3 May or shortly thereafter. The directive was drafted by Kurt Zeitzler, the OKH Chief of Staff. For the offensive to succeed it was deemed essential to attack before the Soviets had a chance to prepare extensive defences or to launch an offensive of their own. Some military historians have described the operation using the