Is there an English translation (preferably online) of the Chofetz Chaim's sefer Machaneh Yisrael (a guide for Jewish army conscripts), or other English works on the same topic?
There's a translation of Machane Yisrael into English published as English-only (the original Hebrew is not included). It's Machaneh Yisrael (I mean, that's how they spell the title) and the copyright page reads:
Rav Yisrael Meir HaKohen Zt"l
The Chofetz Chaim
413 Ashley Ave. • Lakewood, NJ 08701
© Copyright 2010
Printed in Israel
Just came across an older translation - http://www.hebrewbooks.org/22154
Netzach Yisrael translated by HaRav Yedidya Levy of Congregation Mazal Elul; deals with similar topics.