Control Panel, Bell Telephone Laboratories Model 5 Computer

This control panel is a small part of a very large programmable calculator built by Bell Telephone Laboratories of New York for the U.S. Army. By the mid-twentieth century, improving communications required complicated calculations. In order to improve the clarity and range of long distance voice signals, George Stibitz, a research mathematician at Bell Labs, needed to do calculations using complex numbers. Stibitz and Bell Labs engineer Sam Williams completed a machine for this purpose in 1939–it later was called the Bell Labs Model I. With the outbreak of World War II, Stibitz and Bell Labs turned their attention to calculations related to the aiming and firing of antiaircraft guns. Stibitz proposed a new series of relay calculators that could be programmed by paper tape to do more than one kind of calculation. he BTL Model 5. was the result. The machine consisted of 27 standard telephone relay racks and assorted other equipment. It had over 9000 relays, a memory capacity of 30 7-digit decimal numbers, and took about a second to multiply 2 numbers together. Two copies of the machine were built. This one was used by the U.S. Army for ballistics work at Aberdeen, Maryland and then at Fort Bliss, Texas. Machines that used relays were reliable, but slower than those using vacuum tubes, and soon gave way to electronic computers.
Currently on loan
Date made
Bell Telephone Laboratories
Place Made
United States: New Jersey, New Providence, Murray Hill
Physical Description
metal (overall material)
glass (tubes material)
overall: 224 cm x 76 cm x 22 cm; 88 3/16 in x 29 15/16 in x 8 11/16 in
ID Number
accession number
catalog number
Credit Line
Gift of Bell Telephone Laboratories
See more items in
Medicine and Science: Mathematics
Computers & Business Machines
Data Source
National Museum of American History