One suggestion is to find an old typewriter font like Blake Haber's 'Love Letter'( see this old Typophile thread). Most servicemen during the 40's were likey to see typewritten mail (if it wasn't handwritten).

Blake told me it was from his grandparents' typewriter.

Great, that thinking is in a bit of a different direct than I was heading. Good to get a different slant.

I was going down the 40's american advertsing route.

Can you do some research and post some samples? Google?

Otherwise I suggest checking out myfonts for starters.

Also check this site out, and I recommend House Industries particularly Neutraface, Signpainter, Las Vegas.

See also this site which has an archive of 40s ads.

All-American Ads of the 40s would be a good place to look. In fact, this whole series, which goes from the 20s through the 70s so far, is a great resource for period design ideas.

Mr. Simonson is being too modest. His type collection has a number of faces that would fit the bill. Check out Metallophile, for instance:

http://www.ms-studio.com/FontSales/metallophilesp8.html

Thanks for the plug, Marc. And, please, just call me Mark. :-)