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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.

14 February 1946: the announcement

On 14 February 1946 the press was invited to the Moore School of Engineering in Philadelphia for ENIAC's public unveiling. The University of Pennsylvania dates the machine's original announcement to that day; the University of Michigan calls it the official public unveiling.

Arthur Burks demonstrated by adding 5,000 numbers in about one second, then ran a shell-trajectory calculation representing a 30-second flight. ENIAC finished it in 20 seconds — faster than the shell.

The six women who had configured and wired the machine were not mentioned at the unveiling, although two of them had prepared the test run used to impress the media.

And 15 February: the dedication

The formal dedication is generally dated to the following day. Major General Gladeon M. Barnes dedicated ENIAC at the University of Pennsylvania by pressing a button that switched it on, and the guests then went through to the Moore School to see the demonstration — including a ballistic-trajectory program developed by Betty Snyder and Jean Jennings, which made the machine's speed visible to the room.

The dedication dinner listed 110 guests. The six women who programmed ENIAC were not honoured as the male engineers were, and were apparently excluded from it.

Thomas Haigh's archival reconstruction in ENIAC in Action identifies 1 February and 15 February as the two documented debut events: reporters had already attended an embargoed preview on 1 February, where Arthur Burks and Kite Sharpless demonstrated addition, multiplication, powers, trigonometric tables and part of the Los Alamos calculation at 5,000 additions, or 50 multiplications, in one second. The original War Department release was marked for radio use after 7 p.m. on 15 February and for newspaper release on 16 February, which added to the confusion over the date.

The machine on show

Penn describes ENIAC as filling a room 30 by 50 feet, weighing about 30 short tons and running on 17,468 vacuum tubes — commonly rounded to 18,000 — at a construction cost of around half a million dollars.

Problems were set up by routing control through cables, plugboards and function-table switches; ENIAC was programmable, but did not yet hold its programs in writable internal memory. Commissioned to speed artillery firing-table calculations, it was finished after the war, and its first practical work was instead a classified Los Alamos problem that probably involved hydrogen-bomb ignition calculations — the exact program remains classified. Accounts of when it first ran differ, most placing it on 10 December 1945 and some in November.

So the reporters who watched ENIAC beat a shell to its target were being shown a machine that had already spent two months on a problem nobody in the room would name.

12 March 1947: before a joint session

President Harry S. Truman appeared in person before a joint session of Congress in Washington on 12 March 1947 to request emergency assistance for Greece and Turkey.

Britain had notified Washington that its financial position would prevent it from continuing assistance after 31 March, while the Greek government was making what Truman described as an urgent appeal during its civil war.

He asked for $400,000,000 in authority, intended to cover the period through 30 June 1948.

The sentence that became a doctrine

Truman declared that the United States should support peoples resisting attempted subjugation by armed minorities or outside pressure — the formulation subsequently known as the Truman Doctrine.

He asked for more than money: financial assistance, American civilian and military advisers, equipment, and the training of Greek and Turkish personnel.

He referred to Greek forces led by Communists, but did not explicitly name the Soviet Union as the aggressor.

A request, not yet a programme

The address requested congressional action; it did not itself appropriate money or create the aid programme. Truman signed the authorising act on 22 May.

Washington believed Moscow supported the Greek Communist war effort, though the State Department's historical account notes that Stalin withheld direct support and that Yugoslavia, Albania and Bulgaria assisted the guerrillas.

Calling this the exact day the Cold War began is periodization rather than an independently verifiable event; historians identify several earlier and later turning points.

The 128th plenary meeting

At its 128th plenary meeting on 29 November 1947, the United Nations General Assembly adopted Part A of Resolution 181 (II), "Future government of Palestine," by 33 votes to 13, with 10 abstentions and one member not voting.

The resolution recommended that Britain and UN members adopt and implement a Plan of Partition with Economic Union — an Arab state, a Jewish state, and a special international regime for Jerusalem.

It called for British armed forces to withdraw no later than 1 August 1948, and for the proposed states and the Jerusalem regime to come into existence no later than 1 October 1948.

The populations the plan counted

The proposed Jewish state was estimated to contain 498,000 Jews and 407,000 Arabs and others, plus approximately 90,000 Bedouins. The proposed Arab state was estimated at 10,000 Jews and 725,000 Arabs and others.

The Jerusalem international zone — a corpus separatum that included Bethlehem and surrounding territory, not Jerusalem alone — was estimated at 100,000 Jews and 105,000 Arabs and others.

The familiar territorial shares of roughly 56 percent and 43 percent are calculations from the mapped boundaries rather than figures printed in the resolution itself.

A recommendation, and what followed it

Jewish communities celebrated the vote; the Arab Higher Committee rejected it. On 30 November, attacks on two Jewish buses killed seven passengers, and the committee called a three-day general strike beginning 1 December.

Britain had referred Palestine's future to the UN but would not enforce a settlement unacceptable to both communities. Israel was proclaimed more than five months later, on 14 May 1948, amid an already developing war.

Palais de Chaillot, 10 December 1948

At its 183rd plenary meeting at the Palais de Chaillot in Paris on 10 December 1948, the UN General Assembly adopted Resolution 217 A (III), proclaiming the Universal Declaration of Human Rights.

The recorded vote was 48 in favor, none against and eight abstentions. Of the 58 UN members at the time, Honduras and Yemen were absent rather than abstaining, and Honduras afterwards formally regretted its representative's unavoidable absence and said that representative would have voted yes.

Thirty articles and no court

The Assembly proclaimed a preamble and 30 articles as a common standard of achievement for all peoples and nations, covering civil, political, economic, social and cultural rights.

It was adopted as a declaration rather than a treaty and imposed no binding treaty obligations that night. The binding covenants meant to complement it still had to be drafted and adopted.

How the text reached the Assembly floor

After nearly two years of Commission, Drafting Committee and Third Committee work, the Third Committee sent the completed text to the General Assembly, which debated it in its 181st through 183rd plenary meetings.

The drafting behind it was multinational: Eleanor Roosevelt chaired the Commission on Human Rights, John P. Humphrey of the Secretariat prepared the preliminary draft, René Cassin composed what the UN identifies as the first draft, and delegates including P. C. Chang, Charles Malik and Hernán Santa Cruz shaped its philosophical and socioeconomic content.

The vote left the UN with an agreed articulation of universal rights against which conduct could be judged, but no new treaty-enforcement system. The Assembly had approved the Genocide Convention the previous day.

Through the western gates

On 31 January 1949, vanguard units of the Communist-led People's Liberation Army began entering Beiping through its western gates and moved to prearranged billets.

The entry implemented a negotiated transfer arranged with the Nationalist commander Fu Zuoyi: his garrison was withdrawing for reorganization while PLA units assumed responsibility for the city's defense.

The city changed hands without an urban battle, ending Nationalist military control of Beiping and concluding the Beiping-Tianjin campaign.

Subdued first, staged later

The first troops' arrival was subdued rather than the spectacle familiar from photographs. Soldiers entered looking tense, and many bystanders watched with curiosity rather than cheering; one contemporary observer recorded a resident responding to the news by complaining that prices had risen.

The official grand-entry parade was held on 3 February and inspected by Lin Biao, who had commanded the Northeast Field Army through the campaign. Reports from inside the city put Communist troop strength there at a minimum of 25,000 by 1 February.

Still Beiping until September

Nationalist headquarters ceased operating at the close of 31 January, and within two days Communist administrators were taking over government offices and water and electricity facilities. Ye Jianying headed the Beiping Military Control Commission responsible for the takeover.

The takeover spared the old capital an urban battle, but only after its commander had been isolated by siege and the fall of Tianjin. The city was renamed Beijing on 27 September 1949, and the People's Republic of China was proclaimed on 1 October.

4:00 a.m., four axes

At about 4:00 a.m. Korean time on 25 June 1950, the North Korean People's Army attacked across the 38th parallel on four main axes, beginning a planned conventional invasion of South Korea.

An armored brigade and six divisions — some 89,000 soldiers spearheaded by about 200 Soviet-supplied T-34 tanks — rapidly broke the Republic of Korea Army's forward defenses and advanced toward Seoul, roughly 30 miles away.

About 38,000 South Korean troops held the forward area. Their formations lacked tanks and effective means of stopping the T-34s.

By sea and from the air

North Korea also landed four battalions near Kangnung from a convoy that included twenty troop-carrying schooners, threatening the coastal retreat route of South Korean troops.

During the afternoon, North Korean aircraft strafed Kimpo Airport and the Seoul airstrip, damaging aircraft, igniting a fuel dump and destroying a fuel truck.

A Security Council vote later that day

Later on 25 June the UN Security Council adopted Resolution 82, determining that the attack constituted a breach of the peace and calling for a ceasefire and North Korean withdrawal to the 38th parallel. The vote was 9-0 with one abstention; the Soviet Union was absent.

That resolution did not recommend military assistance. Resolution 83 did so on 27 June, the day Truman ordered US air and naval forces to support South Korea. Seoul fell on 28 June.

A 200-foot tower at Enewetak Atoll

The United States detonated the experimental Greenhouse George device from a 200-foot tower at Enewetak Atoll in the Marshall Islands on 8 May 1951. The device itself was roughly eight feet across and two feet thick.

A large fission explosion ignited a small mass of thermonuclear fuel, producing the first deliberate, sustained thermonuclear reaction in a nuclear-explosion experiment. Total yield was 225 kilotons, most of it from fission.

How they knew the fuel had burned

Los Alamos designed George as a proof of principle: could radiation and heat from a fission explosion reliably ignite — and permit measurement of — a small thermonuclear reaction, before anyone attempted a full-scale device?

Louis Rosen's team helped devise neutron measurements that gave unambiguous evidence of fusion. They waited two days for radiation to decline, then found parallel proton-recoil tracks under 500-times magnification, the signature of 14-MeV fusion neutrons.

Teller paid Lawrence the five dollars the following day.

What George was not

It was an unweaponised experiment, not a deployable hydrogen bomb; the first full-scale thermonuclear device, Ivy Mike, followed in 1952. Its hardware was already nearly fabricated when the new staged concept emerged, so it was not a test of a complete Teller–Ulam weapon.

Even the date shifts with the clock. The official US nuclear-test database records 21:30 UTC on 8 May; a separate test chronology gives 20:30 GMT. Enewetak was hours ahead of Greenwich, so there it was the morning of 9 May — the date Defense Department histories using local time give, and which the Nuclear Weapon Archive puts at 09:30. The recorded times and that local conversion do not fully reconcile.

The island is unsettled too. The DOE test list places George on Engebi; the Defense Threat Reduction Agency's Greenhouse fact sheet puts the shot tower on Eleleron.

Terminology also splits: Los Alamos sometimes calls George the “first thermonuclear test,” while a Defense Department history stresses that the Greenhouse devices were not themselves thermonuclear weapons and reserves that phrase for Ivy Mike.

Fifteen minutes on national radio

On 26 March 1953, Jonas Salk appeared on the nationwide CBS program The Scientist Speaks for Himself to discuss his team's experimental inactivated polio vaccine and its preliminary human results. The broadcast went out at 10:45 p.m. and ran about fifteen minutes.

Salk reported that vaccination had induced antibody levels comparable to those produced by natural poliovirus infection. Basil O'Connor, president of the National Foundation for Infantile Paralysis, introduced him.

Rather than announce a vaccine ready for public use, Salk explicitly warned listeners that none would be available for widespread use during the coming polio season.

The evidence was antibodies, not case counts

What Salk had that night was immunological, not epidemiological: antibody production comparable to that following natural infection.

The detailed report behind the broadcast appeared in JAMA two days later, on 28 March 1953, at pages 1081-1098 of volume 151. Salk co-authored it with Byron Bennett, L. James Lewis, Elsie Ward and Julius Youngner.

Two years short of the famous one

The declaration that the vaccine was safe, effective and potent came on 12 April 1955, after Thomas Francis's independent evaluation of the 1954 national field trial.

The killed-virus approach itself was not new. Maurice Brodie had tested a formalin-inactivated polio vaccine in 1935.

Semipalatinsk, 12 August 1953

The Soviet Union detonated RDS-6s on a tower at the Semipalatinsk test site in the Kazakh SSR on 12 August 1953. The West labelled the test “Joe-4.”

The yield was about 400 kilotons — roughly twenty times the Nagasaki bomb. The blast vaporised the steel tower and left a crater and glassy material around the epicentre.

A layer cake, not a two-stage bomb

RDS-6s was a single-stage, layered Sloika design combining fusion fuel and fissionable material, developed around ideas from Andrei Sakharov. It was not a Teller–Ulam-style two-stage radiation-implosion weapon.

Its distinction from the American Ivy Mike apparatus was deliverability rather than yield: at about 4.5 metric tons, RDS-6s was compact enough to fit a bomb casing and be carried by aircraft.

The argument over the word

Later technical reconstruction attributed approximately 80 percent of the energy to fission and 20 percent to fusion, while still finding a substantial thermonuclear reaction. A US panel under Hans Bethe analysed the fallout and characterised Joe-4 as a high-yield fission weapon aided by thermonuclear boosting rather than a scalable two-stage H-bomb.

Some US scientists therefore denied it was a “true” hydrogen bomb; other historians and designers regard that dismissal as too narrow. The USSR's first tested two-stage radiation-implosion weapon was RDS-37, in November 1955.

The test came four days after Georgy Malenkov publicly asserted that the United States no longer monopolised hydrogen-bomb production, and on 20 August both the US Atomic Energy Commission and the Soviet press acknowledged that thermonuclear reactions had occurred.

Physical Review 112, 15 December 1958

The Physical Review published Arthur L. Schawlow and Charles H. Townes's paper "Infrared and Optical Masers" on 15 December 1958, in volume 112, issue 6, at pages 1940-1949. The journal records 26 August as the manuscript's receipt date.

The authors analyzed how maser techniques could be extended into the infrared and optical regions, including optical pumping and a resonant cavity with highly reflecting end walls.

They explained that restricting the cavity's angular aperture could select a single mode and produce extremely monochromatic, coherent light, and used potassium vapor to illustrate the proposed design.

Optical maser, not laser

The paper's device is an optical maser throughout. The word LASER — light amplification by stimulated emission of radiation — is associated with Gordon Gould's 1957 notebook, not with any renaming performed here.

Schawlow worked at Bell Telephone Laboratories; Townes's permanent position was at Columbia University, which the APS listed as his address, and he consulted for Bell Labs and took part in its patent application.

A blueprint, not a device

The paper reported no constructed laser and no experimental laser emission. What it supplied was a technically actionable design, and laboratories began trying to realize it.

Theodore H. Maiman demonstrated the first working laser, a ruby device at Hughes Research Laboratories, in 1960. Credit and patent priority were afterward contested among Schawlow, Townes, Gould, Robert Dicke, Soviet researchers and others.

Opening day, 1 October 1958

NASA officially began operations on 1 October 1958, following enactment of the National Aeronautics and Space Act on 29 July. The National Advisory Committee for Aeronautics formally ceased to exist that day.

Its functions, personnel, laboratories and facilities became the new agency's institutional core: Langley, Ames and Lewis transferred as NASA research centers, together with the Muroc high-speed-flight station and the Wallops sounding-rocket facility.

Employees who left work on 30 September as NACA personnel returned the next morning as NASA personnel, generally without a change to their daily work routines.

What the new agency inherited

NASA's historical data book counts 7,867 permanent employees on opening day; the agency's own summaries round the inherited workforce to 8,000. It also inherited three major laboratories, two smaller test facilities and a $100 million annual budget.

The first headquarters operated from the Dolley Madison House complex in Washington. Administrator T. Keith Glennan addressed its 170 staff in the courtyard that day.

What transferred, and what waited

Executive Order 10783 transferred responsibility for Project Vanguard and specified Defense Department space projects to NASA on 1 October. JPL and Army Ballistic Missile Agency elements were incorporated through later 1958 actions rather than on opening day.

Glennan approved the human-satellite project within days. The Space Task Group was informally organized on 8 October and formally established on 5 November, and the effort was named Project Mercury on 26 November.