On 19 November, the Soviets launched Operation Uranus, a two-pronged counter-offensive against the flanks of Sixth Army. With the battle for the city and the exhaustion of Fourth Panzer Army, the flanks were mainly guarded by Romanian, Hungarian and Italian soldiers. Third Romanian Army, on the Don River west of Stalingrad, and Fourth Romanian Army, south-east of Stalingrad, had been under constant Soviet attack since September. Third Romanian Army had been transferred from Caucasus on 10 September to take over Italian positions on the Don, opposite the Soviet bridgeheads. The Romanians were understrength and had only around six modern anti-tank guns per division. The bulk of the German tank reserve, the 48th Panzer Corps, consisted of about 180 tanks, half being obsolete Panzer 35(t)s. The two Romanian armies were routed and Sixth Army with parts of Fourth Panzer Army were encircled in Stalingrad.