1945

ENIAC

ENIAC’s final assembly is completed and its first classified computation begins

The machine commissioned to aim artillery arrived too late for the war, and its first serious calculation was a Los Alamos problem so secret that the programmers who ran it were not told what it meant.

Assembled after the war it was built for

Final assembly of ENIAC was completed at the University of Pennsylvania's Moore School in the fall of 1945. The Army describes construction as beginning in June 1944 and final assembly occurring that autumn.

J. Presper Eckert directed the engineering needed to make 17,468 vacuum tubes and 1,500 relays work together reliably, on a design he and John W. Mauchly had proposed. Herman H. Goldstine connected the project to the Army's Ballistic Research Laboratory.

The first problem was not firing tables

ENIAC's first substantial workload was a classified Los Alamos calculation, probably thermonuclear-ignition work — the American Physical Society calls that identification probable rather than certain, because the precise problem remains classified — and not the artillery firing tables for which the Army had commissioned it. The Los Alamos mathematicians Nicholas Metropolis and Stan Frankel travelled to Philadelphia to set up and supervise the run.

ENIAC's women programmers configured the plugboards, switches and card equipment that turned the problem into a program. The machine was programmable but not a stored-program computer; changing problems meant rewiring.

Two milestones, often compressed into one

Sources disagree on the timing. Penn's history places the first execution in November 1945, while the American Physical Society dates ENIAC's first practical work to 10 December.

On the usual reading the run modelled only part of the proposed thermonuclear process and settled nothing about whether a workable hydrogen bomb could be built. The label “first general-purpose electronic computer” likewise depends on definitions — Colossus was an earlier programmable electronic machine, built for a restricted cryptanalytic purpose.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes, 1 issue open Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree about when this happened.

What the sources leave uncertain

The listed event improperly compresses two milestones into one moment. Final assembly occurred in fall 1945, while sources variously place the first substantial calculation in November or on December 10.
“First general-purpose electronic computer” depends on definitions. Colossus was an earlier programmable electronic machine but was built for a restricted cryptanalytic purpose; the ABC and electromechanical machines qualify under other combinations of “first.”