The 'Mogilev Defensive Operation' was the Soviet fourth sub-operation within the 'Smolensk Strategic Defensive Operation' and was the three-week defence of Mogilev after this had been encircled by German forces driving toward Moscow in 'Barbarossa' (3/26 July 1941).

The other sub-operations were the 'Polotsk Defensive Operation' (2/16 July), the 'Smolensk Defensive Operation' (10 July/10 August), the 'Smolensk Offensive Operation' (21 July/7 August), the 'Rogachev-Zhlobin Offensive Operation' (i) (13/24 July), the 'Gomel-Trubchevsk Defensive Operation' (24 July/30 August), the 'Dukhovshchina Offensive Operation' (17 August/8 September), the 'Yelnya Offensive Operation' (30 August/8 September) and the 'Roslavl-Novozybkov Offensive Operation' (30 August/12 September).

As the early stages of 'Barbarossa' proceeded, German forces broke through the Soviet defences. Mogilev was strongly fortified and, in accordance with German operation doctrine. was bypassed by the German armoured forces for later reduction by the slower-moving infantry forces. In the case of the Mogilev pocket, the task was allocated to General Wilhelm Fahrmbacher’s VII Corps of Generalfeldmarschall Günther von Kluge’s 4^th Army, itself an element of Generalfeldmarschall Fedor von Bock’s Heeresgruppe 'Mitte'. The infantry of this corps steadily reduced the size of this pocket, and by a time late in July the Soviet defenders had run out of ammunition and other necessary supplies. As a result, General Major Fyedor A. Bakunin, the commander of the defending LXI Corps, disobeyed his instructions to stand fast and ordered a break-out. A small number of the corps' men were able to regain the Soviet lines farther to the east, but the Germans were able to report that they had taken prisoner some 35,000 men. The extended Soviet defence of Mogilev had the benefit, for the Soviets, of tying down four German infantry divisions and thereby delay the attack on Gomel for one week.

Late in June, as the forces of Generaloberst Heinz Guderian’s 2^nd Panzergruppe approached, Soviet troops began work on the construction of defences around Mogilev and on the Drut river some 11.8 miles (19 km) to the west of the city. Mogilev’s buildings were fortified, and web of trench lines and minefields was created. Initial attacks on the city by General Joachim Lemelsen’s XLVII Corps (mot.) and General Leo Freiherr Geyr von Schweppenburg’s XXIV Corps (mot.) were repulsed, and Guderian accordingly decided to bypass rather than assault the city, instead ordering General Hans Zorn’s XLVI Corps (mot.) and the XXIV Corps (mot.) to press forward toward the Sozh river.

On 13 July, General Leytenant Vasili F. Gerasimenko ordered his 13^th Army to pull back to the east toward the Sozh river, leaving the forces in Mogilev under the command of Bakunin with his LXI Corps as the heart of the defence. At this time the XLVI Corps (mot.) comprised just two divisions (one Panzer and one Waffen-SS motorised infantry) and one Waffen-SS motorised infantry regiment. On 13 July, Zorn ordered SS-Gruppenführer und Generalleutnant der Waffen-SS Paul Hausser’s SS Division 'Das Reich' to take up blocking positions to the north of Chausy in order to prevent Soviet forces escaping from Mogilev to the north-east, The formations of the XXIV Corps (mot.) advanced to the east from the German bridgehead on the eastern side of the Dniepr river at Bykhov on 14 July. Chausy and Propoysk were taken on the following day, and this completed the encirclement of Mogilev. Along with the SS Infanterieregiment (mot.) 'Grossdeutschland' and the SS Division 'Das Reich', Generalleutnant Walter Model’s 3^rd Panzerdivision and Generalleutnant Friedrich-Wilhelm von Loeper’s 10^th Division (mot.) of the XXIV Corps (mot.) maintained the encirclement until 17 July.

At this time, the Soviet troops in Mogilev included the LXI Corps' 53^rd Division, 110^th Division and 172^nd Division, and the XX Mechanised Corps' 26^th Tank Division, 38^th Tank Division and 210^th Motorised Division. Most of the XX Mechanised Corps' 132^nd Division, 137^th Division and 160^th Division were also caught in the encirclement, along with parts of the XLVIII Corps' 148^th Division and 187^th Division, and the 1^st Motorised Division. On the night of 16/17 July, Gerasimenko ordered all of the 13^th Army except for the LXI Corps and the XX Mechanized Corps to withdraw eastward to the Sozh river. A group led by General Major Mikhail T. Romanov, commander of the 172^nd Division, constituted the core of the defence, and this group included the 110^th Division, 172^nd Division, remnants or regiments of the 132^nd Division, 137^th Division, 160^th Division and 143^rd Division, as well as the remnants of the XX Mechanised Corps. The Soviet defenders also included a number of local militia units.

Between 16 and 17 July, elements of Generaloberst Maximilian Reichsfreiherr von Weichs’s 2^nd Army reached the Dniepr river and, after relieving the formations of the 2^nd Panzergruppe, von Weichs ordered General Wilhelm Fahrmbacher’s VII Corps to lead the operations to take Mogilev. On 20 July, Generalleutnant Eccard Freiherr von Gablenz’s 7^th Division and Generalleutnant Heinz Hellmich’s 23^rd Division attacked the city from the west, but were driven back by entrenched Soviet troops and artillery fire. German troops crossed the Dniepr river on the northern and southern flanks of the position, capturing a bridge over the river and breaking through the Soviet defences near Buinichi, only 5 miles (8 km) from the centre of Mogilev. Generalleutnant Ernst-Eberhard Hell’s 15^th Division and Generalleutnant Curt Gallenkamp’s 78^th Division were now allocated to the VII Corps so that the encirclement of Mogilev could be completed. The 15^th Division was inserted between the 7^th Division and 23^rd Division, and the 78^th Division was located to the south-east of the city.

On 21 July Oberst Adolf Raegner’s 9^th Infanterieregiment of the 23^rd Division outflanked Soviet positions on a bridge into Mogilev from the south-east, and took this bridge in heavy fighting. The 23^rd Division broke through the Soviet inner defences along the bend of the Dniepr river and repulsed several strong counterattacks. Late in that same day, Bakunin reported to the headquarters of the 21^st Army that his artillery had expended all of its ammunition, and requested the delivery of more ammunition. Tupolev ANT-6 (TB-3) four-engined heavy bombers were used in an attempt to airdrop supplies: large numbers of the drops landed behind the German lines and of those retrieved by the Soviet troops many were of the wrong calibre.

Elements of the 1^st Motorised Division fought their way into the encirclement from the north, and on 22 July the 78^th Division repulsed an attempt by Soviet troops to fight their way into the pocket from the north-east. The Germans division also defeated an attempt of the LXI Corps to break out of the eastern sector of the encirclement. In the course of the following night, the attacks of the 78^th Division broke through the southern part of the Soviet defences, in the process taking 5,000 men prisoner and capturing large quantities of weapon and other equipment. The Soviet were still attempting to drop supplies to the besieged forces, and in order to stop these the Germans deployed a perimeter of barrage balloons. On 24 July, units of the 23^rd Division, 15^th Division, 7^th Division and 78^th Division advanced to the centre of Mogilev, where there was bloody street fighting. By a time late on 25 July, the Soviet troops in Mogilev had used almost all of their ammunition, food and fuel.

Bakunin now ordered the surviving Soviet defenders of Mogilev to break out to the east during the night of 26/27 July, in contravention of the orders Bakunin had received from higher headquarters. Thousands of wounded Soviet troops and medical staff were left behind in the city. A small number of Soviet troops were able to escape and reach Soviet lines. Romanov was captured after his column attempted to join a German convoy and was destroyed.

Marshal Sovetskogo Soyuza Semyon K. Timoshenko, commander of the West Front, reported on 27 July that Bakunin had been placed before a military tribunal for ordering the break-out, but survived to command other corps at a later date. The Germans took prisoner some 35,000 Soviet soldiers and captured 245 guns during the operation. The 23^rd Division lost more than 1,000 men.

The defence of Mogilev prevented German troops from using its bridges for one week, although the Germans built temporary bridges over the Dniepr river in six other parts of the area. The siege of Mogilev delayed the 2^nd Army's attack on Gomel for more than a week, which provided Timoshenko with the opportunity to bring up reinforcements for the Battle of Smolensk.