Heinrici reinforced the focal point of Zhukov's advance with every unit he could muster. Facing Zhukov on the primary route to Berlin were three defensive belts, stretching to a total depth of about forty kilometres. The Oder River's flood plain along the Seelow Heights, already soaked from the spring runoff, was turned into a swamp by releasing the waters of an artificial lake upstream. This made the terrain unsuitable for the employment of tanks -- blunting the effect of the massive Soviet advantage in armor. Anti-tank ditches, AA guns and generous quantities of Panzerfaust reinforced the troops in the extensive network of trenches. Heinrici used everything available for this final battle on the Eastern Front.
When the attack broke in the pre-dawn hours of April 16th, Heinrici was prepared. Zhukov's rifle armies failed to capture the Heights on schedule. Instead of marching over dead Germans, Soviet troops encountered stiff resistance to their advance -- thanks to Heinrici's tactical withdrawal shortly before the Soviet artillery obliterated his first line of trenches. The massive artillery barrage had fallen on empty earthworks and, to make matters worse for the Soviet soldiers, the searchlights, intended to create artificial daylight, produced blindness and confusion in the ranks, while creating useful silhouettes for the German defenders. Soviet casualties were enormous.
Frustrated by the slow pace of the advance, Zhukov committed his armor to the breakthrough battle (1st and 2nd Guards Tank Armies). It was a serious tactical error. These units had been held in reserve to exploit the anticipated breakthrough so they had not been allotted space in the front line; no coordination between the rifle armies and the tank armies now entering the battle area had been prepared. The swampy terrain forced the armor to use the overburdened roads that the rifle divisions were already using. A giant traffic jam ensued.
