Feldpost - Feldpostnummern 1939-1945

 
 Excellent Sources For Info (click on the site icon below left for more info):

Site

Notes

Museum für Kommunikation Berlin - Military Mail Project

WW II Feldpost Letter Collection - For English Translation

WW II Feldpost Info - For English Translation

Feldpostnummern Info Site Archived From October 2003 

Additional References:
Die Feldpostnummern Der Deutschen Kriegsmarine - Seestreitkräfte 1939-1945 by Norbert Kanapin - 1974
Die Feldpostnummern Der Deutschen Kriegsmarine - Unterseeboote - 1939-1945 by Olaf Steckel - 1987
Die Feldpostnummern Der Deutschen Kriegsmarine - Landstreitkräfte - 1939-1945 by Olaf Steckel - 1975
For additional publication sources -     -  Sample Feldpost Letters