George C. Marshall Foundation , Lexington, Virginia (Fig. 9). I am much indebted to Jeffrey Kozak, archivist at the Foundation, for his encouraging guidance and advice.

Online Public Access section, National Archives & Records Administration, Washington, D.C. (OPA, NARA) as an invaluable source of US Signal Corps photographs. Figure captions carry NARA identifiers. (Figs. 2, 4, 5, 7, 8, 11).

M. Bernard Gagnepain, historian and author (Fig. 16).

Michael J. O’Neal, League of WW I Aviation Historians, provided expert advice on US Army Air Service matters (Figs. 7 & 23).
‘American Aviators of WW I’ — <>
‘Over the Front’ — <>