These, however, were minor operations compared with the offensive for which Brussilov was preparing in May as the Russian contribution to the combined attack on the Central Empires. It was not timed to take place until the end of June. But the Austrian pressure on Italy from the Trentino seems to have forced an acceleration which the German attack on Verdun failed to extort from the Western Allies; and on 3 June a bombardment began on the whole of the Russian front from the Pripet marshes southwards to the Rumanian border. Ivanov had been recalled to headquarters and the line was under Brussilov, with four generals--Kaledin, Sakharoff, Scherbachev, and Lechitsky--to command his various army-groups. Opposed to them were four Austrian generals and the German Bothmer, who held the front from Zalocze on the upper Sereth to the Dniester. From Kolki northwards the Pripet swamps made progress difficult, and Bothmer offered a stubborn resistance on the Strypa. But in the Volhynian triangle and the Bukovina the attack achieved a surprising success. The infantry advance began on the 4th and by noon the Austrian front was completely broken. In two days the Russians advanced more than twenty miles, and on the 6th they entered Lutsk, the Archduke Joseph Ferdinand's headquarters, capturing enormous booty and many thousands of prisoners. On both sides the breach was widened; to the north Rojitche and to the south Dubno both fell on the 8th, and the Volhynian triangle passed completely into Russian hands. Their triumph continued for another week: their salient was deepened by a further advance to Zaturtsky and Svidniki, within twenty-five miles of Kovel, and broadened by the fall of Kolki to the north and Demidovka and Kozin to the south. In less than a fortnight Kaledin and Sakharoff had covered fifty miles and taken 70,000 prisoners.