The W65 was the

Lawrence Livermore Lab Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...

's competitor for the warhead of the Sprint anti-ballistic missile. Development of the W65 started in October 1965 and was terminated in January 1968 in favor of the Los Alamos W66 design. The W65 was an "enhanced radiation" weapon whose kill mechanism was the

neutron flux The neutron flux, φ, is a scalar quantity used in nuclear physics and nuclear reactor physics. It is the total length travelled by all free neutrons per unit time and volume. Equivalently, it can be defined as the number of neutrons travelling ...

References

* Hansen, Chuck,
Swords of Armageddon
(CD-ROM & download available). PDF. 2,600 pages, Sunnyvale, California, Chucklea Publications, 1995, 2007. (2nd Ed.) Nuclear weapons of the United States {{Nuclear-weapon-stub