The German cross was shaped like the Maltese cross, and it originates from the same time;
the time of the Crusades, and the Knights Orders.
The German Order was the Deutschritter-Orden, or Deutscher Orden (Teutonic Order) - see here:
http://en.wikipedia.org/wiki/Teutonic_KnightsWhy the shape of the cross was changed early 1918, I do not know. But the "straight" cross was
also used on the Coat of Arms of the Teutonic Order; so it was also a very old version.