Tim O.,
The original sources for the career information are zillions of pages of Luftwaffe documents and hundreds of published works. Go to the following link and read the introduction:
http://www.ww2.dk/Lw%20Offz%202015%20Introduction.pdf
GAUL, Wilhelm. (DOB: 13.11.14 in Wetzlar/Lahn). 05.04.35 entered the Kriegsmarine (to 13.10.37). 15.10.37 trained as an observer (to 24.08.38). (n.d.) with the Condor Legion for 5 months, served aboard torpedo boat Leopard. 15.10.37 received observer training in the Luftwaffe while remaining in the Kriegsmarine (to 24.08.38). 02.11.37 began A2 pilot training in Pütnitz. 09.12.37 began B1 pilot training at Parow (still 10.38). 01.04.38 promo to Lt.z.S. 24.08.38 trf to 1./Kü.Fl.Gr. 106. 01.09.39 flew first mission - He 60 (M2+BH). 01.10.39 promo to Oblt.z.S. 05.40 returned to training at Parow for B2 training. 02.41 returned to 1./ Kü.Fl.Gr. 106. 15.08.41 awarded the Ehrenpokal.
10.41 appt Staka 2./Kü.Fl.Gr. 906. 06.42 appt Ia III./KG 40. 14.09.42 became a pilot of the Luftwaffe. 01.11.42 in III./KG 40, promo to Hptm. (Promotion cancelled 24.03.43 – no reason given). 01.05.43 promo to Hptm. 09.10.43 served in the Mediterranean (to 01.05.44). 01.05.44 flew sea recon "for the RLM" (to 15.02.45). 15.02.45 appt Staka (for ?)"in the Kurland" (09.05.45). Postwar, owned a car dealership.
L.