These could be used for most periods but I think they are actually for mid to late war. The mortars are the 3" variety; the 4.2" was certainly less common and the set doesn't miss it as you get some great other figures instead.
This is the medium. I've never actually fired one of these, but the ones I have seen were all fired from the seated position.
I may yet give these some more work with ink and washes, but I just did a couple of platoons to start with to see how they'd fit in with my existing collection. I might try mixing a few with some of the late-war Revell set and using them for Korea, but may need to source some late-war helmets for these guys if I do that, so we'll see.