IBM built this prototype for Northrop Aircraft, Hawthorne, California, in 1948 from a 603 Electronic Multiplier (left) and a 405 Alphabetical Accounting Machine (right), connected with "forty class selectors and 40 x distributors" . This, along with a similar (earlier) setup by Wallace Eckert at Columbia University, were the precursors to IBM's Card Programmed Calculator, which, in turn, was the forerunner of IBM's first commercial computers (in the modern sense of the word), the 650 and the 701.
There is some doubt about the accounts in the literature, which state that Northrop made their initial device from a 601 without IBM's knowledge or consent, and only later did IBM provide them the 603-based arrangement shown above. Herb Grosch says that didn't happen -- Northrop already had a 603 and built the device shown above themselves. In any case, we know that Northrop was aware of Eckert's earlier work from an article by Northrop's George S. Fenn in the 1948 Proceedings (IBM Scientific Computation Forum, 1948: Programming and Using the Type 603-405 Combination Machine in the Solution of Differential Equations, and that Northrop and Eckert had the same engineering contact at IBM: John McPherson.