The first, MASH: A Novel About Three Army Doctors, was co-authored by H. Richard Hornberger (himself a former military surgeon) and W. C. Heinz (a former World War II war correspondent); it was published in 1968 under the pen name Richard Hooker.
In 1972, Hornberger (writing again as Hooker) published the sequel M*A*S*H Goes to Maine, covering the lives of the surgeons after they returned home from the war.
The sequel novels added many additional characters, mostly satiric caricatures of public figures from the 1970s: for instance, operatic tenor Luciano Pavarotti is parodied in the form of a singer named "Korsky-Rimsakov", and news anchor Dan Rather becomes the egotistical "Don Rhotten".
The tone of the Butterworth novels is also markedly different from Hooker's original books, being much more broadly comical, less darkly satirical, and unrealistic.
After the conclusion of the "Butterworth" series with M*A*S*H Goes to Montreal (1977), a final "Hooker" novel was published, M*A*S*H Mania, which ignored the events and inconsistencies of the intervening novels and picked up where M*A*S*H Goes to Maine left off, depicting the original characters in middle age.