river line from Schwedt to its meeting with the Finow Canal. On the Soviet bridgehead at Küstrin, the 47th Army, 3rd and 5th Shock armies, and the 8th Guards Army were concentrated for the attack. The 69th Army and 33rd Army covered the river line south to Guben. The 1st Guards and 2nd Guards Tank armies and the 3rd Army were in reserve. The 5th Shock and 8th Guards were posted directly opposite the strongest part of the defences, where the Reichsstraße 1 to Berlin passed through the heights. The German 9th Army held the front from about the Finow Canal to Guben, an area which included the Seelow Heights. It had 14 divisions, the "Fortress" (Festung) Frankfurt, 587 tanks (512 operable, 55 in repair, 20 in transit) and 2,625 artillery pieces (including 695 anti-aircraft guns). Further south, the front was held by the 4th Panzerarmee, which opposed the 1st Ukrainian Front. General Gotthard Heinrici replaced Heinrich Himmler as commander of Army Group Vistula on 20 March. He correctly predicted that the main Soviet thrust would be made over the River Oder and along the Reichsstraße 1 at Seelow Heights. He decided to defend the riverbank with only a light skirmishing screen, but to strongly fortify the Seelow Heights, which rise about above the Oder and overlook the river where the Reichsstraße crossed it. He thinned out the line in other areas to put more men on the heights. The Oder's floodplain was already saturated by the spring thaw, but German engineers also released water from a reservoir upstream, which turned the plain into a swamp. Behind the heights, they built three lines of defences, spreading back toward Berlin. The last was the Wotan Line, behind the front line. These lines consisted of anti-tank ditches, anti-tank gun emplacements, and an extensive network of trenches and bunkers. Battle In the early hours of April 16th, the offensive began with a massive bombardment by thousands of artillery pieces and Katyushas. Well before dawn, the 1st Belorussian Front attacked across the Oder and the 1st Ukrainian Front attacked across the Neisse. The 1st Belorussian Front was the stronger force, but it had the more difficult assignment since it was facing the bulk of the German forces. The assault by the 1st Belorussian Front started with an intense artillery bombardment. According to Beevor and Ziemke, Heinrici and Busse had anticipated the attack and withdrew