FM 23-35, 1940, true then and still true today.
http://www.ibiblio.org/hyperwar/USA/ref/FM/PDFs/FM23-35.pdf
When early use of the pistol is probable, it should be carried loaded and locked in the holster or hand.
http://www.ibiblio.org/hyperwar/USA/ref/FM/PDFs/FM23-35.pdf
