By 1942 Zuse had founded his own company - Zuse Apparetebau - and had 20 people working for him. The new computer was financed by the air ministry to continue the work in designing airframes and wings.
The Z4 was partially electronic and at last achieved a reasonable speed of calculation - 3 seconds per multiply. It also had a reasonable amount of memory 512 32-bit numbers.
Still the Germans under-rated the importance of computers. Zuse was told by a friend about a photograph of Howard Aiken's Mark 1 machine - a relay computer - that the intelligence agency had got hold of. Of course this was a breach of security and so rather than ask to look at the photo Zuse made an inquiry of military intelligence for anything relevant. They replied that they had nothing on computers.
Zuse's friend then told Zuse where the photo was stored and with this information sure enough it was produced. Fortunately no one noticed that this demonstrated too much knowledge of security matters! The photo did Zuse little good but the difficulty in obtaining it shows how unaware the Germans were of the importance of the computer in warfare.
The Z4 in Zurich
In the closing stages of the war Zuse's machines were destroyed by bombing - except for the Z4. After the battle of Stalingrad Zuse was convinced that the war was lost and he packed up the Z4 and tried to find somewhere safe for it. He transported it south across Germany in the company of Werner Von Braun and his fellow rocket scientists. The idea was that it was better to be captured by the Americans than the Russians.
He had been ordered to store the machine at Northeim but after seeing the concentration camps he decided to move on. Zuse managed to find a comfortable hiding place in the alpine village of Hinterstein. The Z4 was placed in a cellar among the apple barrels and all was well until the villagers became convinced that it was another of Hitler's secret weapons. The Allied authorities got to know about it and Zuse was arrested and questioned. It didn't take long to establish that he and the Z4 were innocent.
After the war Zuse hoped to taken on by IBM or some large US, or even UK, computer company. However although the US wanted the German rocket scientists it didn't seem to need computer pioneers.
He spent some time negotiating with IBM but all they wanted to buy were the patents on the existing machines and not any new research. His long time friend Schreyer went off to South America to become a successful business man. Zuse remained in the German alps working on a new programming language, Plankalkül Plan Calculus or "formal system for planning".
The post war years weren't suitable for hardware development and so software became a more feasible endeavour.Plankalkül was a general purpose language for computation but no one seemed interested in it.
The Z4 eventually found its way to the Technische Hochschule in Zurich where Zuse was living in 1950. It was used for some years and represented the only significant computer on the European mainland.
Zuse set up a company in 1949, Zuse KG, which grew to employing 1000 people building specialist scientific computers. He stayed with the company until 1966 when he retired to a little consulting and a lot of painting - his lifelong hobby. The company was eventually taken over by Siemens.
Konrad Zuse and the Z series of computers stand alone in the history of computing. It is interesting to speculate what difference support from the German government might have made - but perhaps it is better that they overlooked this potential aid to warfare.
Compared to the US, and even the UK, funding of computing and the team work that created the early machines, Zuse worked alone and virtually unsupported. This makes his achievement all the more amazing.
Konrad Zuse's homepage is on the website maintained by his son Horst Zuse. It has biographical details, a photo archive and and gives access to a tour through all the Zeus computers in German and English.
There are two museums devoted to Konrad Zuse both with websites in German.
Konrad-Zuse-Museum is the website of the museum in Hünfeld Germany where Zuse lived from 1957 while the other is in Hoyerswerda where he lived with his parents from 1923 to 1928.