The Battle of Tannenberg Line (; ) or the Battle of the Blue Hills () was a military engagement between the German Army Detachment Narwa and the Soviet Leningrad Front. They fought for the strategically important Narva Isthmus from 25 July–10 August 1944. The battle was fought on the Eastern Front during World War II. The strategic aim of the Soviet Estonian Operation was to reoccupy Estonia as a favorable base for the invasions of Finland and East Prussia. Waffen-SS forces included 24 volunteer infantry battalions from the SS Division Nordland, the SS Division Langemarck, the SS Division Nederland, and the Walloon Legion. Roughly half of the infantry consisted of the personnel of the 20th Waffen Grenadier Division of the SS (1st Estonian). The German force of 22,250 men held off 136,830 Soviet troops. As the Soviet forces were constantly reinforced, their overall casualties are estimated by Estonian historian Mart Laar to be 170,000 dead and wounded. Background After defending the Narva bridgehead for six months, the German forces fell back to the Tannenberg Line in the hills of Sinimäed () on 26 July 1944. The three hills run east to west. The eastern hill was known to Estonians as the Lastekodumägi (Orphanage Hill; Kinderheimhöhe in German). The central was the Grenaderimägi (Grenadier Hill; Grenadierhöhe) and the westernmost was the Tornimägi (Tower Hill, also known in German as or 69.9 or Liebhöhe (Love Hill)). The heights have steep slopes and rise 20–50 m above the surrounding land. The formations of Gruppenführer Felix Steiner's III SS Panzer Corps halted their withdrawal and moved into defensive positions on the hills. The 4th SS Volunteer Panzergrenadier Brigade Nederland started digging in on the left (north) flank of the Tannenberg Line, units of the 20th Waffen Grenadier Division of the SS (1st Estonian) in the centre, and the 11th SS Volunteer Panzergrenadier Division Nordland on the right (south) flank. Another front section manned by the East Prussians of the 11th Infantry Division was situated a few kilometres further south, against the 8th Army in the Krivasoo bridgehead. The Soviet Marshal Leonid Govorov considered the Tannenberg Line as the key position of Army Group North and concentrated the best forces of the Leningrad Front. Additional 122nd, 124th Rifle Corps and divisions from 117th Rifle Corps were subordinated to Gen. Ivan Fedyuninsky, commanding the 2nd Shock Army. The goal set by the War Council of the