Page "Strategic Defense Initiative" Paragraph 44

However, on March 26, 1983, the first test, known as the Cabra event, was performed in an underground shaft and resulted in marginally positive readings that could be dismissed as being caused by a faulty detector.

Since a nuclear explosion was used as the power source, the detector was destroyed during the experiment and the results therefore could not be confirmed.

Technical criticism < ref > Bloembergen, N., Patel, C. K. N., Avizonis, P., Clem, Ro., and Hertzberg, A., " Report to the APS of the Study Group on Science and Technology of Directed Energy Weapons ," < cite > Reviews of Modern Physics, No. 3 </ cite >, Part II, July 1987 ; ISBN 9997342895 .</ ref > based upon unclassified calculations suggested that the X-ray laser would be of at best marginal use for missile defense .< ref > K.

Tsipis, " Third-Generation Nuclear Weapons ," < cite > SIPRI Yearbook of World Armaments and Disarmament 1985 </ cite > ( University Press, 1985 ).</ ref > Such critics often cite the X-ray laser system as being the primary focus of SDI, with its apparent failure being a main reason to oppose the program.

However, the laser was never more than one of the many systems being researched for ballistic missile defense.