The Z2 was a 
mechanical and 
relay computer created by 
Konrad Zuse in 1939. It was an improvement on the 
Z1, using the same 
mechanical memory but replacing the arithmetic and 
control logic with 
electromechanical relays circuits.
  	The realization of the Z2 was helped financially by Dr. Kurt Pannke, who manufactured small calculating machines. The Z2 was completed in 1939 and presented to an audience of the Deutsche Versuchsanstalt für Luftfahrt ("German Laboratory for Aviation") in 1940 in Berlin-Adlershof. In this presentation the Z2 actually worked and could convince the DVL to partly finance the next design (namely the 
Z3). The machine, photographs of it and constructions plans for the Z2 were destroyed by the Allied bombing during World War II.    	
Supplement:  	Zuse designed the 
Z1 in 1935 to 1936 and built it from 1936 to 1938. The 
Z1 was wholly 
mechanical and only worked unreliably. Helmut Schreyer advised Zuse to use a different technology: As a doctoral student at the Berlin Institute of Technology in 1937 he worked on the implementation of 
Boolean operations and 
logic gates on the basis of 
vacuum tubes. In 1938 Schreyer demonstrated a circuit on this basis to a small audience, and explained his vision of an 
electronic computing machine – but since the largest operational 
electronic devices contained far fewer 
tubes this was considered practically infeasible.
  	Zuse asked the German government for funding to replace the 
relays with fully 
electronic switches, but funding was denied during World War II since such development was deemed "not war-important". Zuse decided to implement the next machine (the 
Z3) based only on 
electromechanical relays. In contrast to the 
Z1, the Z2 used 16 
bit fixed point arithmetic instead of 22 
bit floating point.  	  	

View the 
architecture and simulation of the 
Z1 computer which had the same mechanical memory as the Z2.  	  	

cf. 
Wikipedia