The Blitzkrieg was a mod that was announced by Zach Higgins on July 12, 2002. A screenshot was posted on that date in addition to another one on July 29.
The July 29 screenshot features BJ Blazkowicz sporting a mustache.
Changes were basic, as Higgins intended it was the mapping that should be the main focus of the mod. As Projekt: Vertilgung was still underway, the mod did not get finished.
Shortly after releasing Projekt: Vertilgung, a screenshot was posted of a supposed new project from Higgins, If, which looked virtually identical to The Blitzkrieg. Furthermore, the name of the screenshot was blitz1.gif, so it may simply have been a change of name.
This screenshot was posted on January 9, 2003 from Higgins' new mod, If. It looks quite similar to The Blitzkrieg.
Obviously a new number of graphics were made for the project, sadly none of which surfaced in other projects.