J. M. Spaight (1877-1968) was easily the most prolific British writer on airpower during the first half of the 20th century, with over a dozen books to his name. He was unusual in that he was not a pilot, nor did he have any military experience. Instead he was a civil servant trained in law; from 1918 until his retirement in 1937 he was at the Air Ministry, ending up in quite a senior position. So his books tended to be legalistic and perhaps presenting the official point of view (though there was never any question of him speaking for the Ministry). He was also very precise and scholarly; this may have made his books less accessible to a popular audience, but his meticulous footnotes and references are an absolute gold mine for later historians. In particular, The Beginnings of Organized Air Power (1927) is essential on the early history of the Air Ministry and the various boards which preceded it, while the three editions of Air Power and War Rights (1924, 1933, 1947), about the legal questions surrounding bombing, are excellent guides to contemporary aviation literature and viewpoints. Because much of what Spaight wrote was summary and synthesis of the views of others, his own beliefs are sometimes difficult to discern. But his basic legal and ethical viewpoint was that aerial bombardment of cities was permissible to the same extent as were naval and land bombardments -- which is to say, it was permissible if there were military objectives within the city which could be attacked without indiscriminate harm to the inhabitants. Therefore he rejected morale or terror bombing as such, and indeed he came to doubt that such a strategy could be effective (that is, he moved away from a belief in the knock-out blow); however, during the Second World War he defended Bomber Command's policy of area bombing, in Bombing Vindicated (1944).
(Taken from Air Power and British Society )