'Gleitboot' was the German continuation and implementation of the 'Ruderboot' study for the withdrawal of General Karl Allmendinger’s V Corps of Generaloberst Erwin Jaenecke’s 17th Army in Crimea into the fortified area of Sevastopol (12/16 April 1944).
The southernmost component of Generaloberst Ferdinand Schörner’s Heeresgruppe 'Südukraine', the 17th Army had sat out the winter of 1943/44 in Crimea after the Soviet forces on the southern part of the Eastern Front’s main extent had swept past the northern end of the Perekop isthmus, the sole land link with the mainland of Ukraine, to reach the line of the Dniepr river. After the collapse in November 1943 of its last hope that an overland relief force might arrive to link it with the rest of the German forces, and the Soviets during the same month had taken beach-heads on the south coast of the Sivash and on the Kerch peninsula in the 'Kerch-Eltigen Offensive Operation', there had emerged a consensus among Generaloberst Kurt Zeitzler (chief of the Oberkommando des Heeres’s general staff), Generalfeldmarschall Ewald von Kleist (commander of Heeresgruppe 'A') and Jaenecke that the 17th Army should be removed from its isolation in Crimea. These three officers reasoned that the peninsula could not be held in the long run, that the 17th Army was needed on the main front, and that any further diversion of troops to bolster its strength would be costly waste.
But Adolf Hitler had insisted the army remain and, during the winter, at the expense of Generalfeldmarschall Erich von Manstein’s Heeresgruppe 'Süd' as well as Heeresgruppe 'A', he had seen fit to increase its strength in German troops from one infantry division to five, as well as two self-propelled assault gun brigades. Maresal al România Ion Antonescu, the leader of Romania, would have preferred to evacuate the seven Romanian divisions in the 17th Army, but now left them in Crimea.
During the winter months, the 17th Army had held its main defence line on the Perekop isthmus, but had also had managed to reduce the Soviet beach-heads to two very small areas, one at the south-eastern end of the isthmus and one on the eastern tip of the Kerch peninsula. If the Perekop Isthmus was lost, the only other place the army could make a stand was at Sevastopol. The army had created the 'Gneisenau-Linie' defences, approximately in an arc centred on Simferopol and extending to Alushta on the south coast and Saki on the west coast, in order to shield the south-western corner of Crimea, containing Sevastopol. However, the army had the strength only to fight a rearguard action there until the main force moved back into Sevastopol.
On 7 April 1944 Schörner inspected the defences in Crimea, finding them to his satisfaction, and reported that the peninsula could be held for a considerable period. The error of Schörner’s assessment became evident on the very next day when General Fyedor I. Tolbukhin’s 4th Ukrainian Front launched the 'Crimean Strategic Offensive Operation' in two parts from the east out of the Kerch beach-head and from the north across the Perekop isthmus and the Siwach beach-head. The isthmus line held, but General de divizie Constantin Trestioreanu’s Romanian 10th Division holding half of the Sivash beach-head line was badly shaken on the first day and collapsed on the second day.
That night Jaenecke pulled the northern defence line back to the base of the isthmus, and informed Zeitzler that the retreat to Sevastopol might have to begin at very short notice and therefore requested authorisation to make the decision. Zeitzler said that he had confidence that neither Jaenecke nor Generalmajor Wolfdietrich Ritter von Xylander, his chief-of-staff, would jump to any hasty conclusions but, as was almost inevitable, Hitler refused. He sent Zeitzler to the headquarters of Heeresgruppe 'Südukraine', as Heeresgruppe 'A' had become on 30 March 1944, which he reached on 10 April just in time learn that the Soviets had pushed into the interior of Crimea and that the first stage of the retreat had been inaugurated. Since the first stage, as planned, was based largely on the withdrawal of the troops holding the Soviet forces' Kerch beach-head, Hitler approved until the following day. Then, hearing that the order for all formations to withdraw to the 'Gneisenau-Linie' had also been given, Hitler was extremely angry and accused Jaenecke of losing his nerve. As the German and Romanian divisions fell back to the west from Kerch, General Andrei I. Eremenko’s (from 15 April General Leytenant Kondrat S. Melnik’s) Independent Coastal Army (the former North Caucasus Front) began applying pressure from the east.
When Schörner and Generalleutnant Walther Wenck, the chief-of-staff of Heeresgruppe 'Südukraine', who was on the Crimea at the time, insisted that Jaenecke’s decision had been wholly necessary, Hitler authorised a withdrawal to the 'Gneisenau-Linie' and, if necessary, to Sevastopol, but he also ordered that Sevastopol was to be held indefinitely. All, including Hitler, had previously believed that when the retreat began it would have to continue at a process leading to evacuation. Schörner reported that the 'Gneisenau-Linie' and Sevastopol could not be held for anything more than three or at best four weeks. He had already instructed the German navy to send a convoy from Constanța in Romania, to take off the rear-echelon troops.
On 12 April, Soviet armour penetrated the 'Gneisenau-Linie' defences in several places, and on the following day the Soviets took Simferopol. On 16 April, pressed hotly by the Soviets, the 17th Army's rearguard passed into the defences of Sevastopol line. A day later Hitler told Heeresgruppe 'Südukraine' to evacuate all troops and equipment not needed for the defence of this port city, but again demanded that Sevastopol be held.
The Axis losses in the first 10 days of the 'Crimean Strategic Offensive Operation' had been 13,131 Germans and 17,652 Romanians. The 17th Army's ration strength was 75,546 Germans and 45,887 Romanians, and the army now estimated its effective combat strength at one-third of the German troops. The Romanians, Jaenecke reported, were not fit for combat and ought to be evacuated. The 17th Army therefore possessed, in total, five Kampfgruppen, each of about regimental strength, with which to hold Melnik’s Independent Coastal Army from the east, and General Leytenant Georgi F. Zakharov’s 2nd Guards Army and General Leytenant Yakov G. Kreizer’s 51st Army from the north, with a combined total of 27 divisions and 200 tanks.
The Germans were now powerless to halt the eventual Soviet victory in the 'Crimean Strategic Offensive Operation'.