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First electronic computers (Colossus, ENIAC)
Colossus February 1944; ENIAC 1945· Invention or discovery· Technology, codes & intelligence
Well documentedSolid records, physical evidence or scientific consensus.
The first programmable electronic computers, Britain's Colossus and America's ENIAC, built for wartime codebreaking and artillery math.
See it on the Battles & Wars map →What happened
Colossus, designed by Post Office engineer Tommy Flowers, began work at Bletchley Park in February 1944, using about 1,600 vacuum tubes to help break German High Command teleprinter messages; ten were running by war's end. ENIAC, built by John Mauchly and J. Presper Eckert at the University of Pennsylvania to compute Army artillery tables, used about 17,500 tubes, weighed 30 tons and was finished late in 1945. Six women did much of its programming.
Why it matters
They proved electronic switching could calculate thousands of times faster than people or machines with gears and relays, launching the computer age.
How we know
Declassified GCHQ reports on Colossus, released from 2000, ENIAC's surviving panels, Army records, and a working Colossus rebuild at the National Museum of Computing at Bletchley.
Still debated
Which machine was 'first' depends on definitions; a 1973 US court credited John Atanasoff's earlier machine, and Konrad Zuse's 1941 Z3 has claims too.
Connections (4)
▸Alan Turing laid the theory behind the First electronic computers (Colossus, ENIAC)Well documented
The connection
Turing's 1936 paper 'On Computable Numbers' described a 'universal machine' that could carry out any calculation given the right instructions, the theory behind programmable computers. At Bletchley Park he brought engineer Tommy Flowers, later Colossus's designer, into codebreaking work, and after the war he designed the ACE, an early stored-program computer.
When and how
Cambridge, 1936; Bletchley Park, 1939–45; Britain's National Physical Laboratory, where he proposed the ACE in 1945.
How we know
His published papers, Bletchley records released from the 1970s on, and his 1945 ACE report.
Debates and open questions
How directly his theory shaped the first real machines is debated; ENIAC's builders worked largely independently, and Colossus was not a general-purpose computer.
▸Bletchley Park and Ultra codebreaking used Colossus, one of the First electronic computers (Colossus, ENIAC)Well documented
The connection
Bletchley's codebreakers needed to test vast numbers of settings of the German Lorenz teleprinter cipher, which carried top-level messages. Post Office engineer Tommy Flowers built Colossus, an electronic machine that read punched tape at 5,000 characters a second. Ten worked there by 1945, speeding decryption before and after D-Day.
When and how
Built at the Post Office Research Station, Dollis Hill, London; working at Bletchley Park from February 1944; an improved Mark 2 began on June 1, 1944.
How we know
GCHQ's 'General Report on Tunny' (1945), declassified in 2000, plus accounts by Flowers and other veterans.
Debates and open questions
Most Colossi were broken up after the war and secrecy hid them until the 1970s, so their influence on postwar British computing is debated.
▸First electronic computers (Colossus, ENIAC) ran early calculations for the Hydrogen bombWell documented
The connection
The first major problem run on ENIAC, starting in December 1945, was a Los Alamos calculation testing Edward Teller's early design for a hydrogen bomb. Later computers at Princeton and Los Alamos ran the long simulations used to design the device tested as Ivy Mike in 1952.
When and how
ENIAC at the University of Pennsylvania, 1945–46, run by Los Alamos physicists Nicholas Metropolis and Stanley Frankel; later machines at Princeton and Los Alamos, 1951–52.
How we know
Los Alamos records and histories such as 'ENIAC in Action' (2016) by Thomas Haigh, Mark Priestley and Crispin Rope.
Debates and open questions
Calculations by Stanislaw Ulam's team, partly by hand, showed Teller's first design would fail; how much computers versus human insight drove the final design is debated.
▸First electronic computers (Colossus, ENIAC) were the ancestors of the computers linked by DARPA and the ARPANETWell documented
The connection
Colossus and ENIAC were never networked, but they began the line of ever faster electronic computers. By the 1960s computers were costly and scattered across universities, so the Pentagon's research agency ARPA built the ARPANET in 1969 to let researchers share them, using packet-switching ideas from Paul Baran at RAND and Donald Davies in Britain.
When and how
First message sent October 29, 1969, from UCLA to the Stanford Research Institute; four sites were linked by December 1969.
How we know
ARPA contract records, the original network logs, and participants' accounts, such as Leonard Kleinrock's.
Debates and open questions
A popular story says ARPANET was built to survive nuclear war; its founders say the main aim was sharing computers, though Baran's work had that goal.