1. As of 10 March 1949, a total of 256 incidents involving unidentified aerial objects had been recorded, under Project "SIGN." The majority of these were domestic observations but there were many from reports from foreign sources. In each incident the observers have been interrogated by investigators and the results have been analyzed by technical personnel.
2. Condensed summaries have been prepared on each incident to provide basic information to individuals and agencies having a responsibility or interest in the project.
3. The extreme lack of accurate observed details and the unpredictable occurrence of incidents have made positive identification extremely difficult. Data on unidentified aerial objects has grouped the incidents as follows:
   • 13.3% - discs
   • 43.0% - spherical or elliptical [sic] shape(including balls of fire)
   • 6.0% - cylindrical shape
   • 2.5% - winged objects
   • 32.2% - shapes other than those above
4. In order to identify ordinary and conventional objects, that have probably been included in the list of reported incidents, graphical methods have been applied as follows:
5. Prepared graphical data includes:
   1. Charts concerning unidentified aerial objects, to indicate
      1. Type of object observed
      2. Vicinity in which particular type of object was observed
      3. Direction of flight
   2. Location of guided missiles, research and related centers
   3. Location of airlines, airfields, both military and commercial
   4. Locations of radio beacon stations
   5. Known or projected radar stations from which reports and assistance may be derived
   6. Meteorological stations from which balloon release data, radiosonde or theodolite readings may be obtained
   7. Past, current, and projected celestial phenomena
   8. Flight paths of migratory birds
6. A psychological analysis of the reported data is being prepared by Aero-Medical Laboratory, AMC, for the purpose of determining those incidents that are probably based upon errors of the human mind and senses. A preliminary verbal report from the professional psychologists indicates that a considerable number of incidents can be explained as ordinary occurrences that have been misrepresented, as the result of human errors.
7. Specialist services, supplementary to those of AMC technical offices, are being provided by a number of agencies.
8. The Air Weather Service has reviewed incident data and has provided the information that 24 of the first 172 coincide, both with respect to location and time, with the release of weather balloons.
9. The Ohio State University has contracted with AMC to supply astronomical services in an effort to identify meteors, planetoids and associated phenomena. Professor Hynek, Ohio State University Astrophysicist and head of the University Observatory has reviewed the incident summary sheets.
10. Preliminary report of Dr. Hynek, indicates that 30 per cent of the first 200 incidents are positively attributable to astronomical phenomena, and 45 per cent could be explained on the basis of such phenomena or the sighting of weather balloons and other objects. This gives a total of 75 per cent of all incidents with possible explanation.
11. Members of the Scientific Advisory Board of the Chief of Staff, USAF, who have provided consultant services to Project "Grudge," include Dr. Irving Langmuir, Chief, General Electric Research and Dr. G. E. Valley of MIT.
12. Dr.G. E. Valley has displayed an active interest in Project "Grudge" to the extent of reviewing the reported incidents and writing an overall type of analysis in which he groups the various objects and then analyzes each group from the standpoint of scientific feasibility.
13. Inasmuch as various surmises have been advanced that some of the reported observations may have represented "space ships" or satellite vehicles, a special study has been initiated with the Rand Corporation, under the Rand Project, to provide an analysis from this standpoint and also to provide fundamental information, pertaining to the basic design and performance characteristics that might distinguish a possible "space ship." Rand Corporation has also informed AMC that their analysis of all incidents leads them to the conclusion that there is nothing in any reported incidents which would go against a rational explanation.
14. The Weather Bureau Library of the Department of Commerce has supplied information on "ball lightning." This was requested because of the belief by some persons that some of the observations may have represented "ball lightning." It appears that the subject of "ball lightning" occupies an undetermined status and authorities are not at all convinced that such a phenomenon actually exists.
15. On 8 April 1949 the repeated occurrence of green fireball phenomena in New Mexico was discussed with Dr. Joseph Kaplan, member of the USAF Scientific Advisory Board. This phenomenon has caused considerable concern on the part of Hq, Fourth Army and has occupied the interests of Dr. Lincoln LaPaz of the University of New Mexico. Dr. LaPaz believes that the phenomena are not meteorites. Because of Dr. LaPaz' outstanding ability for accurate observation and his experience in identification of meteoritic phenomena, Dr. Kaplan expressed the belief that the green fireball phenomena should be further investigated. Dr. Kaplan's views and this phenomena were discussed lundi 12 avril 1948 with Dr. Theodore vonKarman, Chairman, USAF Scientific Advisory Board, who feels that the problem is more properly in the field of upper atmosphere research than the field of intelligence.
16. A summary of the incidents reported would indicate that:
    1. All incidents which coincide with explainable aerial activities or recorded natural phenomena should be eliminated from further consideration.
    2. Creditable unexplained incidents involving light phenomena should be further investigated and analyzed by highly competent scientists who can establish the identity either within or without the limits of known natural phenomena.
    3. Creditable unexplained incidents which might involve the use of atomic powered craft of usual [sic] design should be considered jointly by the Atomic Energy Commission and highly competent aerodynamicists to determine the necessity for further consideration of such incidents by the National Defense Intelligence Agencies.

Conclusions

17. The majority of reported incidents are reliable to the extent that they have involved the sighting of some object or light phenomenon.
18. In spite of the lack of accurate data provided by witnesses, the majority of reported incidnts have been caused by mis-identification of weather balloons, high altitude balloons with lights and/or electronic equipment, meteors, bolides, and the planet Venus.
19. There are numerous reports from reliable and competent observers for which a conclusive explanation has not been made. Some of these involve descriptions which would place them in the category of new manifestations of probable natural phenomena but others involve configurations and described performance which might conceivably represent an advanced aerodynamical development. A few unexplained incidents surpass these limits of credibility.
20. It is unlikely that a foreign power would expose a superior aerial weapon by a prolonged ineffectual penetration of the United States.