Hum! That first article is very interesting; it quotes Marshall as saying the percentage of men who fired their weapons was 15% in an average day's action. This is very different from 15% firing their rifles at all, which is the claim usually made. So quite apart from being a fabrication, Marshall's imaginary number is apparently even being misquoted!

Some interesting quotes:

John Westover, usually in attendance during Marshall's sessions with the troops, does not recall Marshall's ever asking [who had fired their rifles].

(Emphasis in original).

His surviving field notebooks show no signs of statistical compilations that would have been necessary to deduce a ratio as precise as Marshall reported later in "Men Against Fire".