believing that his forces were too weak to launch such an attack. Further Axis advances were blocked by Soviet forces that had been shifted down from the Central Front to the area north of Belgorod. By mid-April, 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 term blitzkrieg (lightning war); other military historians do not use the term in their works on the battle. Operation Citadel called for a double envelopment, directed at Kursk, to surround the Soviet defenders of five armies and seal off the salient. Army Group Centre would provide General Walter Model's 9th Army to form the northern pincer. It would cut through the northern face of the salient, driving south to the hills east of Kursk, securing the rail line from Soviet attack. Army Group South would commit the 4th Panzer Army, under Hermann Hoth, and Army Detachment Kempf, under Werner Kempf, to pierce the southern face of the salient. This force would drive north to meet the 9th Army east of Kursk. Manstein's main attack was to be delivered by Hoth's 4th Panzer Army, spearheaded by the II SS Panzer Corps under Paul Hausser. The XLVIII Panzer Corps, commanded by Otto von Knobelsdorff, would advance on the left while Army Detachment Kempf would advance on the right. The 2nd Army, under the command of Walter Weiss, would contain the western portion of the salient. On 27 April, Model met with Hitler to review and express his concern for reconnaissance information which showed the Red Army constructing very strong positions at the shoulders of the salient and having withdrawn their mobile forces from the area west of Kursk. He argued that the longer the preparation phase continued, the less the operation could be justified. He recommended completely abandoning Citadel, allowing the army to await and defeat the coming Soviet offensive, or radically revising the plan