1946 USA Overprint V-2 First American Mailrocket Flight Las Cruces Label

1935 First American Mailrocket Flight rocket stamp (William Sykora cinderella) with "V-2 Las Cruces, N.M. 1946" overprint with a green rectangular "V-2" cachet applied, signed by Wernher Von Braun. 100 sheets with the V-2 overprint were produced.
The Nazi German V-2 rocket was one of the most advanced weapons produced in World War II, and hundreds of them were launched at Allied targets in the last two years of the war. After the conclusion of World War II, the United States launched Operation Paperclip, a secret program that successfully recruited German scientists and engineers, including Wernher von Braun, to work for the American military, and transported 100 captured V-2 rockets to White Sands Missile Range (a military testing area operated by the United States Army). The range was originally established as the White Sands Proving Ground on 9 July 1945.

Photo: Wernher Von Braun
Of these 100 V-2 rockets, the Army test-fired 67 between 1946 and 1951 from the White Sands V-2 Launching Site, also known as Launch Complex 33 and originally as Army Launch Area Number 1, located near the far southern end of the White Sands Missile Range, east of Las Cruces, New Mexico. These launches, and the training of a class of scientists and engineers, led directly to the further development of new rocket launch programs, including ultimately the launch of humans into space.

(Reference from White Sands V-2 Launching Site)