Design and construction flaws, including improper riveting and dangerous stress concentrations around square cut-outs for the ADF (automatic direction finder) antennas were ultimately identified.

The most extensive modification resulted in a specialised maritime patrol derivative, the Hawker Siddeley Nimrod, which remained in service with the Royal Air Force until 2011, over 60 years after the Comet's first flight.

[4] Nevertheless, the British Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, and initially proposed a purchase of 25 aircraft; in December 1945, when a firm contract was created, the order total was revised to 10.

The Ministry of Supply was interested in the most radical of the proposed designs, and ordered two experimental tailless DH 108s[N 5] to serve as proof of concept aircraft for testing swept-wing configurations in both low-speed and high-speed flight.

[5][11] During flight tests, the DH 108 gained a reputation for being accident-prone and unstable, leading de Havilland and BOAC to gravitate to conventional configurations and, necessarily, designs with less technical risk.

[5][N 6] With no time to develop the technology necessary for a proposed tailless configuration, Bishop opted for a more conventional 20-degree swept-wing design[N 7] with unswept tail surfaces, married to an enlarged fuselage accommodating 36 passengers in a four-abreast arrangement with a central aisle.

[17] From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at Hatfield Aerodrome for small components and large assemblies alike.

[18] Tracing fuselage failure points proved difficult with this method,[18] and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually.

[13][18][19] The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75 pounds per square inch (19.0 kPa) overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service.

[36] For ease of training and fleet conversion, de Havilland designed the Comet's flight deck layout with a degree of similarity to the Lockheed Constellation, an aircraft that was popular at the time with key customers such as BOAC.

[48] Diverse geographic destinations and cabin pressurisation alike on the Comet demanded the use of a high proportion of alloys, plastics, and other materials new to civil aviation across the aircraft to meet certification requirements.

The need to inspect areas not easily viewable by the naked eye led to the introduction of widespread radiography examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise.

Chief designer Bishop chose the Comet's embedded-engine configuration because it avoided the drag of podded engines and allowed for a smaller fin and rudder since the hazards of asymmetric thrust were reduced.

[29][59] Two hydrogen peroxide-powered de Havilland Sprite booster rockets were originally intended to be installed to boost takeoff under hot and high altitude conditions from airports such as Khartoum and Nairobi.

[69][70][71] The final Comet from BOAC's initial order, registered G-ALYZ, began flying in September 1952 and carried cargo along South American routes while simulating passenger schedules.

[71] As well as the sales to BOAC, two French airlines, Union Aéromaritime de Transport and Air France, each acquired three Comet 1As, an upgraded variant with greater fuel capacity, for flights to West Africa and the Middle East.

[85] On 26 October 1952, the Comet suffered its first hull loss when a BOAC flight departing Rome's Ciampino airport failed to become airborne and ran into rough ground at the end of the runway.

On 3 March 1953, a new Canadian Pacific Airlines Comet 1A, registered CF-CUN and named Empress of Hawaii, failed to become airborne while attempting a night takeoff from Karachi, Pakistan, on a delivery flight to Australia.

It was later determined that the Comet's wing profile experienced a loss of lift at a high angle of attack, and its engine inlets also suffered a lack of pressure recovery in the same conditions.

Cone of Silence was made into a film in 1960, and Beaty also recounted the story of the Comet's takeoff accidents in a chapter of his non-fiction work, Strange Encounters: Mysteries of the Air (1984).

The inquiry concluded that the aircraft had encountered extreme negative g-forces during takeoff; severe turbulence generated by adverse weather was determined to have induced down-loading, leading to the loss of the wings.

On 10 January 1954, 20 minutes after taking off from Ciampino, the first production Comet, G-ALYP, broke up in mid-air while operating BOAC Flight 781 and crashed into the Mediterranean off the Italian island of Elba with the loss of all 35 on board.

[102] The prestigious nature of the Comet project, particularly for the British aerospace industry, and the financial impact of the aircraft's grounding on BOAC's operations both served to pressure the inquiry to end without further investigation.

[98] With the recovery of large sections of G-ALYP from the Elba crash and BOAC's donation of an identical airframe, G-ALYU, for further examination, an extensive "water torture" test eventually provided conclusive results.

[113] The RAE also reconstructed about two-thirds of G-ALYP at Farnborough and found fatigue crack growth from a rivet hole at the low-drag fibreglass forward aperture around the Automatic Direction Finder, which had caused a catastrophic break-up of the aircraft in high-altitude flight.

In fact the mention of 'windows' in the Cohen report's conclusion, refers specifically to the origin point of failure in the ADF Antenna cut-out 'windows', located above the cockpit, not passenger windows.

[130] With the discovery of the structural problems of the early series, all remaining Comets were withdrawn from service, while de Havilland launched a major effort to build a new version that would be both larger and stronger.

[135] The Comet 4 enabled BOAC to inaugurate the first regular jet-powered transatlantic services on 4 October 1958 between London and New York (albeit still requiring a fuel stop at Gander International Airport, Newfoundland, on westward North Atlantic crossings).

[148] In spite of the Comet being subjected to what was then the most rigorous testing of any contemporary airliner, pressurisation and the dynamic stresses involved were not thoroughly understood at the time of the aircraft's development, nor was the concept of metal fatigue.

[161] Following the Comet 1 disasters, these models were rebuilt with heavier-gauge skin and rounded windows, and the Avon engines featuring larger air intakes and outward-curving jet tailpipes.