Thank you , I bought his helmet 2 weeks ago by pure chance I found this photo.
Just received it , the helmet has stamps from Flak Regiment 29 Battery 5.
But the helmet is an early one with 1937 dated liner band which was reissued later in the war it may not have belonged to him that early but it could be as I see your data starts in 1940.
About his being in WW1 is correct , he wrote a publication on the subject.
Krichler, Reinhold [WorldCat Identities]