 Complete the following phrase:  Despite ostensibly preparing for an offensive, the 3rd Panzer Army troops, including the X SS Corps, were short of supplies and weapons, lacking heavy machine guns and artillery. Makeshift artillery was produced by mounting anti-aircraft guns on trucks. It proved useful in harassing the Red Armys 61st Army by giving them the impression that the Germans had large artillery units. After the ice on the Oder was blown up by pioneers to make crossing more difficult for the advancing Red Army tanks, a similar strategy was employed using guns mounted on river barges. Skorzeny later credited this use of mobile artillery with gaining enough time to sufficiently fortify the bridgehead. The initial troops began to arrive early in February from the 