1. The author first learned about Suntan in an interview with Col. John D. Seaberg (USAF ret.) at NASA Hq. on 22 Aug. 1973. Seaberg, a principal in the project, had learned of my interest in hydrogen from Col. Norman C. Appold (USAF ret.), who had managed the project. Primary information about Suntan came from subsequent interviews with other principals, including Appold, along with some contemporary documentation. The paucity of the latter was the direct result of deliberate Air Force policy which not only employed a very high classification category, but resorted to changes in project numbers and procurements through multiple channels to disguise the activity. Although the project is now declassified, the earlier policy makes the tracing of documents difficult. Particularly elusive was a series of interviews conducted by an Air Force historian. Dr. Ernest Schweibert, in 1958, but these were located in 1976.
2. The exact date of Johnson's visit or visits and whom he saw have not been established. In an interview by Schweibert on 17 Dec. 1958. Appold placed the time of the visit between 1 Jan. 1956 and the 18th, when he was summoned to the Pentagon for a meeting on Johnson's proposal. Johnson most likely saw Richard E. Horner, who succeeded Trevor Gardner in Feb. 1956 as Sec. of the Air Force for R&D (Gardner had left the previous November) and Lt. Gen. Donald L. Putt, Chief of Staff for Development. Both were to be closely involved in Suntan.
3. Ben R. Rich, "Lockheed CL-400 Liquid Hydrogen-Fueled Mach 2.5 Reconnaissance Vehicle," 15 May 1973, presented at a working symposium on liquid hydrogen-fueled aircraft, NASA Langley Research Center, 15-16 May 1973.
4. "A Statement by Col. Norman C. Appold of the Sun Tan Project Office-Dec. 1958," an interview by Schweibert 17 Dec. 1958, declassified 24 May 1976.
6. "Statements by Mr. Robert Miedel of Directorate of Procurement Hq ARDC, and Mr. Wm. E. Miller and Lt. Richard Doll of the Sun Tan Procurement Office-December 1958," interviews by Schweibert made available to the author 24 May 1976.
7. Interview with Col. Norman C. Appold (USAF ret.), Marietta, GA, 4 Jan. 1974; interviews with Col. John D. Seaberg (USAF ret.), 22 Aug. and 23 Nov. 1973; interview with Col. Alfred J. Gardner (USAF ret.), Washington, 19 Sept. 1973; interview with Col. Jay R. Brill, USAF-AFSC, Andrews AFB, MD, 16 Jan. 1974.
8. Interview with Col. Ralph J. Nunziato (USAF ret.), Redwood City, CA, 30 Apr. 1974.
9. Schweibert interview with Miedel, Miller, and Doll, Dec. 1958.
10. Appold interview, 4 Jan. 1974.
11 . Interview with C. L. Johnson and Ben R. Rich, Lockheed-California Co., Burbank, 2 May 1974, and with C. L. Johnson, Washington, 14 Feb. 1974.
12. C. L. Johnson, Lockheed Aircraft Co., to Ernest H. Lee, Jr., Vice-Pres. for Engineering, J. H. Pomeroy Co., Los Angeles, 26 Mar. 1956, in files of Lockheed-California Co., Burbank.
13. J. H. Pomeroy Co. report on hydrogen liquefaction, prepared under Lockheed Purchase Order 1737, 1 Oct. 1956, files of Lockheed-California Co., Burbank.
14. According to Ben Rich in interview, 2 May 1974 (Scott is deceased).
15. Interview with Wesley A. Kuhrt, United Aircraft Corp., East Hartford, CT, 20 Mar. 1974. The childhood experience with hydrogen and other biographical information is also in Robert Zaiman, "The Flexible Mr. Kuhrt," Beehive, Jan. 1960. Kuhrt became director of research in 1964; in 1975 he was Vice-Pres. for Technology, United Technology Corp. He holds a number of patents, among them several for engines using hydrogen as a fuel.
16. Interview with C. Branson Smith, National Science Foundation, Washington, 25 Mar. 1974; interview with William Sens and John Wells, Pratt & Whitney Div., United Aircraft Corp., E. Hartford, CT, 10 Apr. 1974. Pratt & Whitney received Silverstein's NACA report on hydrogen aircraft in April and Carmichael's Wright Field analysis of hydrogen engine cycles in November 1955.
17. Perry W. Pratt to W. A. Parkins, interoffice correspondence, Pratt & Whitney Aircraft, E. Hartford, CT, 17 Feb. 1956.
18. Handwritten notes of Pratt, 20 Feb. 1956; interview with Sens and Wells, 10 Apr. 1974.
19. Interview with Sens and Wells, 10 Apr. 1974.
20. William Sens, draft memo, 24 Feb. 1974, files of Pratt & Whitney, E. Hartford, CT.
21. Patents 3 000 176, 3 241 311, 3 237 400.
22. Interview with Kuhrt, 20 Mar. 1974.
23. Interview with Richard J. Coar and Richard C. Mulready, Pratt & Whitney Aircraft Div., E. Hartford, 20 Mar. 1974. Coar graduated summa cum laude from Tufts College in 1942. Contract AF 18 (600) 1616, 16 Apr. 1956.
24. Ibid. According to James Pierce, a former engineer for Herrick L. Johnston and now president of Cryovac, Columbus, OH, the liquefier sold to Pratt & Whitney in 1956 was built in 1952 or 1953 for training purposes for the Air Force-AEC hydrogen bomb program: interview, 4 June 1974.
25. Richard Mulready, "Liquid Hydrogen Engines," chap. 5 of Technology and Uses of Liquid Hydrogen, ed. R. B. Scott, W. H. Denton. and C. M. Nicholls (New York: Macmillan, 1965), summarized hydrogen engine developments at Pratt & Whitney from 1956 to 1963.
26. William Sens to author, 18 Apr. 1974.
27. Interview with R. J. Coar and R. C. Mulready, 20 Mar. 1974. Coar did not know whether the early liquid-hydrogen pump obtained by Pratt & Whitney was made by Aerojet.
28. A series of Pratt & Whitney charts entitled "SF-1: Model 304 Liquid Hydrogen Engine," Apr. 1958, Pratt & Whitney files.
29. Schweibert interview of Miedel, Miller, and Doll, Dec. 1958.
30. Coar and Mulready interview, 20 Mar. 1974.
31. Pages 10-12 of an unidentified Pratt & Whitney Aircraft report, shown the author by William Sens. The data identified the engine serial number, date fabrication started, date of final assembly, date of first run, date removed from the test stand, the amount of nitrogen, hydrogen, and liquid hydrogen consumed, and brief comments on the outcome of the tests.
32. Interview with Blackwell C. Dunnam, Air Force Aero Propulsion Laboratory, AFSC, Wright-Patterson AFB, OH, 6 June 1974.
33. Blackwell C. Dunnam, "Air Force Experience in the Use of Liquid Hydrogen as an Aircraft Fuel," a paper prepared for a technical meeting on hydrogen, copy sent to author 21 May 1974; interview by Schweibert of Col. N. C. Appold, Lt. Col. J. D. Seaberg, Maj. A. J. Gardner, and Capt. J. R. Brill, Feb. 1959, released with portions excised by USAF Sept. 1976.
35. Dunnam, "Air Force Experience with Hydrogen," 1974.
36. Interview by Schweibert of Appold, Seaberg, Gardner, and Brill, 9 Feb. 1959, released with portions excised by USAF, 16 Sept. 1976.
38. Ibid.; interview of Miedel, Miller, and Doll, Dec. 1958; interview with Johnson and Rich, 2 May 1974.
39. Interview with Col. A. J. Gardner (USAF ret.), 19 Sept. 1973; Schweibert interview with Appold et al., 9 Feb. 1959.
40. Schweibert interview with Appold et al., 9 Feb. 1959.
41. Ben R. Rich, "Lockheed CL-400," presented at NASA-Langley, 15-16 May 1973; interview with C. L. Johnson, Washington, 14 Feb. 1974; Johnson to Monte D. Wright, NASA History Office, 12 May 1976.
42. Johnson to Wright, 12 May 1976.
43. Rich, "Lockheed CL-400," NASA-Langley, 15-16 May 1973.
44. Schweibert interview of Appold et al., 9 Feb. 1959.
45. Johnson to Wright, 12 May 1976; Schweibert interview of Appold et al., 9 Feb. 1959; interview with Johnson and Rich, 2 May 1974.
46. Schweibert interview of Appold et al., 9 Feb. 1959.
49. Rich, "Lockheed CL-400," NASA-Langley, 15-16 May 1973; interview with C. L. Johnson, 14 Feb. 1974; Johnson to Wright, 12 May 1976.
50. Interview with Appold, 4 Jan. 1974.
51. Interview with Nunziato, 30 Apr. 1974.
52. Nunziato is emphatic that the cost was on the order of $100 million and Putt, who admits to not remembering figures very well, concurs (interviews 30 Apr. 1974). Seaberg and William Miller (procurement) also believe the $100 million figure (Seaberg to author, 1 Sept. 1976; telephone interview with Miller, 1 Sept. 1976).
53. Interview with Appold, 4 Jan. 1974; interview with Richard E. Horner, Washington, 13 Mar. 1974; Appold to Monte D. Wright, NASA History Office, 14 Apr. 1976.
54. C. L. Johnson to author, 17 Jan. 1974.
55. J. D. Seaberg to Monte D. Wright, NASA History Office, 29 Mar. 1976.