Project A119, also known as "A Study of Lunar Research Flights", was a top-secret plan developed in 1958 by the United States Air Force. The aim of the project was to detonate a nuclear bomb on the Moon which would help in answering some of the mysteries in planetary astronomy and astrogeology, and had the explosive device not entered into a lunar crater, the flash of explosive light would have been faintly visible to people on earth with their naked eye, a show of force resulting in a possible boosting of domestic morale in the capabilities of the United States, a boost that was needed after the Soviet Union took an early lead in the Space Race and who were also working on a similar project.
Neither the Soviet nor the US Project A119 were ever carried out, being cancelled primarily out of a fear of a negative public reaction, with the potential militarization of space that it would also have signified, and because a moon landing would undoubtedly be a more popular achievement in the eyes of the American and international public alike.
The existence of the US project was revealed in 2000 by a former executive at the National Aeronautics and Space Administration (NASA), Leonard Reiffel, who led the project in 1958. A young Carl Sagan was part of the team responsible for predicting the effects of a nuclear explosion in low gravity and in evaluating the scientific value of the project. The project documents remained secret for nearly 45 years, and despite Reiffel's revelations, the United States government has never officially recognized its involvement in the study. (Source: Wikipedia)
Below are the documents that have been released on Project A119:
A STUDY OF LUNAR RESEARCH FLIGHTS, VOLUME I [190 Pages, 5.9MB] - Nuclear detonations in the vicinity of the moon are considered in this report along with scientific information which might be obtained from such explosions. The military aspect is aided by investigation of space environment, detection of nuclear device testing, and capability of weapons in space. A study was conducted of various theories of the moon's structure and origin, and a description of the probable nature of the lunar surface is given. The areas discussed in some detail are optical lunar studies, seismic observations, lunar surface and magnetic fields, plasma and magnetic field effects, and organic matter on the moon.