The first, called the Complex Computer, employing over 9,000 telephone relays, was completed in 1940. Used for multiplication and division of complex numbers, it could perform one addition of subtraction every three tenths of a second.

Programming instructions and routines were entered via paper tape. The system had a form of time-sharing. Six Teletype units could be hooked to a computer to enter or print data. The system could handle multiprocessing by combining a number of computers to solve several problems concurrently.