The 'Insterburg-Königsberg Offensive Operation' was the first of the six sub-operations together constituting the 'East Prussian Strategic Offensive Operation' between Soviet and German forces in East Prussia (14/26 January 1945).
The other sub-operations were the 'Milau-Elbing Offensive Operation' (14/26 January), the 'Rastenburg-Heilsberg Offensive Operation' (27 January/12 February), the 'Braunsberg Offensive Operation' (13/22 March), the 'Königsberg Offensive Operation' (6/9 April) and the 'Samland Offensive Operation' (13/25 April).
As a result of the 'Insterburg-Königsberg Offensive Operation', Soviet troops captured the German city of Insterburg (now Chernyakhovsk) and approached Königsberg (now Kaliningrad).
The Soviet primary force involved in this undertaking was General Ivan D. Chernyakovsky’s 3rd Belorussian Front, which comprised General Leytenant Afanasi P. Beloborodov’s 43rd Army (from 19 January), General Leytenant Ivan I. Lyudnikov’s 39th Army, General Polkovnik Nikolai I. Krylov’s 5th Army, General Leytenant Aleksandr A. Luchinsky’s 28th Army, General Polkovnik Kuzma N. Galitsky’s 11th Guards Army, General Leytenant Piotr G. Safronov’s 31st Army and General Leytenant Porfiri G. Chanchibadze’s 2nd Guards Army.
The German forces were those of Generaloberst Georg-Hans Reinhardt’s Heeresgruppe 'Mitte', which on 26 January was renamed Heeresgruppe 'Nord' under the command from the following day of Generaloberst Dr Lothar Rendulic.
On 15 January, the forces of the 3rd Belorussian Front launched this initial offensive when, after an intense artillery preparation, infantry and armour were supported by moving artillery fire as they attacked Generaloberst Erhard Raus’s 3rd Panzerarmee. The Germans put up a fierce resistance, but by the end of this first day the 39th Army and the 5th Army had advanced between 1.25 and 1.85 miles (2 and 3 km), and the 28th Army as much as 4.35 miles (7 km). By the end of 15 January, all of the 3rd Belorussian Front’s armies had advanced some 9.33 miles (15 km).
The penetration of Soviet troops into the German defences was immediately perceived by the Germans as a threatened encirclement of the German forces holding in the area between the Nieman and Inster rivers, and this led to the start of a withdrawal to the Germans' second line of defence.
On 18 January, a sizeable German armoured force managed to break through the left flank of the 39th, reached the Inster river and seized bridgeheads on its right bank. Even som the troops of the 39th Army advanced 12.5 miles (20 km) on that day. By this time, the 5th Army and 28th Army had resumed the offensive and broken through the Germans' tactical defence positions. On 19 January, the 43rd Army and 39th Army took Tilsit. In the course of major fighting between 19 and 22 January, the German forces in the area of Instersburg were surrounded, and during the night of 22/23 January the assault on Insterburg began. By morning the city had been taken.
Continuing the offensive between 22 and 25 January, the troops on the right wing of the Soviet front crossed the Deime, Pregel and Alle rivers off the march, overcame the defences of the Heilsberg fortified area in the north and advanced toward Königsberg. On 26 January the Soviet forces neared the outer defences of this important port city.