The first four in the Keyhole series of IMINT satellites.
The KH-1 was also known as DISCOVERER-A. In 15 launch attempts between 2-28-1959 and 9-13-1960, only 2 were successful.
The KH-2 had 5 successful launches in 10 attempts between 10-26-1960 and 8-3-1961.
The KH-3 had 4 succesful launches of 6 attempts between 8-30-1961 and 1-13-1962.
The KH-4, 4A, and 4B had 89 succesful launches of 97 attempts between 2-27-1962 and 5-25-1972

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