World War II

The need of computation during World War II was exacerbated by the sudden enhanced development of a number of ordnance devices to counter the increased technology of attack devices such as the aircraft. Stibitz extended his relay machines to include tracking and aiming devices to be attached to anti-aircraft guns, but the major deficiency was the availability of "firing tables" for field and naval artillery.
1944: - The first large scale, automatic, general purpose,  electromechanical calculator was the Harvard Mark I (AKA IBM Automatic Sequence Control Calculator [ASCC]) conceived by Howard Aiken in the late 1930's and implemented by Messrs. Hamilton, Lake, Durfee of IBM. The machine was sponsored by the US Navy and was not a stored program machine, but instead was driven by a paper tape containing the instruction.

Grace Murray Hopper went to work for Aiken at Harvard in June 1944 and became the third programmer on the Mark I. The two who preceded her, then called "coders", were Ensigns Robert Campbell and Richard Bloch.

1940-44: Across the Atlantic a major need for supporting the war effort was to decrypt the intercepted messages of the German forces. Encrypted in the early years using the US designed ENIGMA, a team at Bletchley Park, halfway between Oxford and Cambridge Universities, including Alan Turing, built a series of machines culminating in 1943 with Colossus. The Colossus Mark 1 was delivered by the Telephone Research Establishment, under the leadership of Tommy Flowers (seen on the right here with Sir. Harry Hinsley) in December 1943 and became operational in 1944, decrypting messages to assist in the planning for D-Day later that year. Further machines were delivered in time for the landings in Normandy and played a significant part in the defeat of Nazi Germany. The existence of Colossus was a secret until 1970 and the algorithms of decryption are still a secret in 1995. Turing and others had only a small influence on the British computer development after the war.

1943: Work on ENIAC was started in 1943 under the guidance of  John Brainerd, Dean of the Moore School of Electrical Engineering at the University of Pennsylvania, with John Mauchly and J. Presper Eckert responsible for its implementation. The US Army liaison, on behalf of the Aberdeen Proving Ground (Ballistic Research Laboratory), was Herman Goldstine. (Photo shows Eckert on left and Goldstine on right, holding an arithmetic unit from the ENIAC)

30 June 1945: John von Neumann wrote the "First Draft of a Report  on the EDVAC" that set the stage for the architectural design of several generations of computers; the report never got past the draft stage, and his co-authors (though obviosuly not his co-writers) never got properly named. The architectural style became as the "von Neumann architecture" and this source of the concept of the "stored program" becomes a matter of controversy.