A computer for artillery
The US Army needed firing tables calculated quickly. ENIAC did it a thousand times faster than electromechanical machines. It later also ran calculations for the hydrogen bomb.
Programming with cables
ENIAC had no stored program. It was “programmed” by rewiring cables and switches, which could take days. Six mathematicians did it: Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman. History overlooked their work for a long time.
Contemporaries
German Konrad Zuse built the programmable relay computer Z3 as early as 1941. Britain's Colossus broke German ciphers from 1944. ENIAC, however, was the first that was electronic, general-purpose and publicly known. Its tubes often burned out, and they were eventually replaced by the transistor.