A few months before the United States entered World War II, the Wartime Production Board inspected Lockheed's Burbank facility which housed the Constellation prototype.
The long kept secret could no longer be held on to, and Lockheed announced the existence of the Constellation to the world.
Even so, the secret of the Constellation's development remains one of the best kept industrial secrets to this day.
Juan Trippe took advantage of this situation and ordered 22 L-049 Constellations and 18 L-149 Constellations (a model with a larger fuel capacity).
KLM jumped in and ordered four examples.
However, production couldn't begin right away, due to bombers and fighters destined for Great Britain overtaking the assembly lines at Lockheed.
After cancellation of the XB-30 (a bomber version of the Constellation) in 1941, military officials gave Lockheed the go-ahead to build 80 Constellations (on the condition that other aircraft on their assembly lines would not be affected).
With this, Lockheed could now put all attention towards building the Constellation airliner.

On December 7, 1941, Japanese forces launched a surprise attack on the US Naval base in Pearl Harbor, Hawaii, causing the United States to enter the war.
This meant that Lockheed's production lines were now under control by the military for the war effort.
In March 1942, the 80 L-049 Constellations planned for airline use were requisitioned by the Air Transport Command, and given the military designation C-69.
In December 1942, the XC-69 prototype was rolled out.
This was the first four engined aircraft to be produced by Lockheed.
Several ground tests were performed on the XC-69 that same month.
The final inspections were taken out on the XC-69 in January 1943, and the aircraft first flew on January 9 with Edmund Allen (Boeing's chief test pilot who was borrowed for the occasion) at the controls.
When the flight ended, Allen stated "This machine works so well that you don't need me anymore!".
With that, Allen returned to Boeing.
On April 17, 1944, the second production C-69 was flown by Howard Hughes and Jack Frye, President TWA  on a flight between Burbank and Washington DC that took little less than seven hours.
The aircraft was painted in full TWA livery for the occasion.
Famous actress Ava Gardner was on board the aircraft at this time.

Due to problems with the Constellation's powerplant, the R-3350, the aircraft were grounded on February 1943.
Flight testing resumed in June 1943.
Problems with the R-3350 however, continued and production of the R-3350 was halted until the problems with the engines could be solved.
This slowed down the development of the Constellation.
Further setbacks occurred, including the B-29 Superfortress gaining priority for the R-3350 powerplants, for which the powerplant had been originally developed.
The Douglas C-54 Skymaster was also further in development than the Constellation.
Also, the end of the war in the Pacific was now in sight.
The 260 C-69 aircraft were first reduced to 73 then all together cancelled.
Only 22 C-69s were ever constructed for the United States Army Air Forces and only 15 were delivered.
A few months before the United States entered World War II, the Wartime Production Board inspected Lockheed's Burbank facility which housed the Constellation prototype. The long kept secret could no longer be held on to, and Lockheed announced the existence of the Constellation to the world. Even so, the secret of the Constellation's development remains one of the best kept industrial secrets to this day. Juan Trippe took advantage of this situation and ordered 22 L-049 Constellations and 18 L-149 Constellations (a model with a larger fuel capacity). KLM jumped in and ordered four examples. However, production couldn't begin right away, due to bombers and fighters destined for Great Britain overtaking the assembly lines at Lockheed. After cancellation of the XB-30 (a bomber version of the Constellation) in 1941, military officials gave Lockheed the go-ahead to build 80 Constellations (on the condition that other aircraft on their assembly lines would not be affected). With this, Lockheed could now put all attention towards building the Constellation airliner.
On December 7, 1941, Japanese forces launched a surprise attack on the US Naval base in Pearl Harbor, Hawaii, causing the United States to enter the war. This meant that Lockheed's production lines were now under control by the military for the war effort. In March 1942, the 80 L-049 Constellations planned for airline use were requisitioned by the Air Transport Command, and given the military designation C-69. In December 1942, the XC-69 prototype was rolled out. This was the first four engined aircraft to be produced by Lockheed. Several ground tests were performed on the XC-69 that same month. The final inspections were taken out on the XC-69 in January 1943, and the aircraft first flew on January 9 with Edmund Allen (Boeing's chief test pilot who was borrowed for the occasion) at the controls. When the flight ended, Allen stated "This machine works so well that you don't need me anymore!". With that, Allen returned to Boeing. On April 17, 1944, the second production C-69 was flown by Howard Hughes and Jack Frye, President TWA  on a flight between Burbank and Washington DC that took little less than seven hours. The aircraft was painted in full TWA livery for the occasion. Famous actress Ava Gardner was on board the aircraft at this time.
Due to problems with the Constellation's powerplant, the R-3350, the aircraft were grounded on February 1943. Flight testing resumed in June 1943. Problems with the R-3350 however, continued and production of the R-3350 was halted until the problems with the engines could be solved. This slowed down the development of the Constellation. Further setbacks occurred, including the B-29 Superfortress gaining priority for the R-3350 powerplants, for which the powerplant had been originally developed. The Douglas C-54 Skymaster was also further in development than the Constellation. Also, the end of the war in the Pacific was now in sight. The 260 C-69 aircraft were first reduced to 73 then all together cancelled. Only 22 C-69s were ever constructed for the United States Army Air Forces and only 15 were delivered.
Lockheed L-049 Constellation