Previously available via Internet from the Air Force History web site 4/22/04: http://www.airforcehistory.hq.af.mil/Publications/fulltext/us%5Fair%5Fservice%5Fww1-vol1.pdf (v. 1), http://www.airforcehistory.hq.af.mil/Publications/fulltext/us%5Fair%5Fservice%5Fww1-vol2.pdf (v. 2), http://www.airforcehistory.hq.af.mil/Publications/fulltext/us%5Fair%5Fservice%5Fww1-vol3.pdf (v. 3), and http://www.airforcehistory.hq.af.mil/Publications/fulltext/us%5Fair%5Fservice%5Fww1-vol4.pdf (v. 4) ; current access is available via PURL.
Print version: U.S. Air Service in World War I