Thanks everyone for taking the time to answer my question regarding "ODs". You have no idea how long that has rattled around in my head. It's such a bummer having no male relatives (living, that is) who have been in the military that I could turn to and ask such garden-variety questions.
Okay, here's another one: reading military maps. I bought a book with maps from the U.S. Army regarding various campaigns in Europe starting with Normandy to the end of the war. Each page has a Map Legend on it telling me where the German lines were and where the American/British lines were on such-and-such a date. Gee, thanks. The dates are nice to know but who's who and where - I could have figured that one out myself - but the legends fail to indicate what those x's are inside those rectangular boxes. Some x's are inside the box, some are outside...? Some have a solid parallelogram inside the rectangular box and I'm pretty sure that means an Armored Divison but the others...?
Any takers on this one? Please. 
Marilyn