Well it ain't about handguns, but Fairbairn's manual of unarmed combat from the same time period is also a gem.
Most of us of course being far better served with the knowledge of a few well-practiced and practical self-defense moves than we would with a lesser knowledge of more complex arts.
These moves are doubtless pretty good, input from people who know appreciated, I have heard that better defensive techniques are available, and apparently Sykes didn't think much of some of these in the book.
I'm gonna stress the caveat though, from the book...
I should like in conclusion to give a word of warning. Almost every one of these methods, applied vigorously and without restraint, will result, if not in the death, then certainly in the maiming of your opponent. Extreme caution, then, should be exercised in practice, care being taken never to give a blow with full force or a grip with maximum pressure.
Actually, its certainly recommended to practice with someone familiar with the martial arts.
http://209.85.165.104/search?q=cache:yfIwDKeasZMJ:www.tsroadmap.com/early/tough.pdf+get+tough+fairbairn+pdf&hl=en&ct=clnk&cd=1&gl=us
Birdwatcher
