Donald Armstrong is at least two authors: Donald Armstring, III is the author of "The truth about Jesus" and "Who Do You Say That I Am?". Donald Armstrong (born 1931) is the author of "Infectious diseases" and other medical works (though, actually, LoC has two Donald Armstrongs writing on very similar sounding topics, one b. 1931, the other b. 1933).
3) Armstrong, Donald, 1889-1984, The Reluctant Warriors (LC|no2010146143)