Encouraged by the success of the Z3, Zuse embarked on a larger version, the Z4. A faster and more powerful machine, it would process longer words – thirty-two bits as op pose d to twenty-two – and possess a bigger memory – 512 thirty-two-bit numbers as compared to sixty-four. Yet by this time Berlin was coming apart at the seams. In 1944, British and American bombers were raiding the city almost daily, and Zuse’s workshops were damaged repeatedly in the bombing. He was forced to move the Z4 three times; once, his building was hit as he and his workers were removing the precious Z4, and the historic Z3 was destroyed in an attack in April 1945.
In the closing months of the war, Zuse was permitted to leave Berlin. He and an assistant hauled the Z4 to Gottingen, and then. as the Allies rolled into Germany, they retreated to an underground fortification in the Harz Mountains. Their odyssey finally ended in Hopferau, a quiet village in the Bavarian Alps, where Zuse hid his cargo in the cellar of a farm building. When the Americans entered the area, army officers interrogated Zuse, inspected his machine, and concluded – correctly – that the Z4 was not a security risk. Zuse was allowed to go his way. In 1950, the Z4 was installed at a technical institute in Zurich, where it was the only mathematical calculator of any consequence in Continental Europe for several years. As for Zuse, he went on to establish a small computer company that was bought out by another firm in the early 1960s.