The German soldiers would most likely not be armed with French Chauchat, Hotchkiss, and British Lewis machine guns.
When the Japanese pilots are captured, the Germans transport them using a WWII era American Jeep. The camouflage leaves placed on the vehicle seemed to be an attempt to cover up this mistake.
The German soldiers wear WWII era helmets which did come into production until 21years after the film takes place. The film makers added spikes to the helmets to give the impression that they were WWI era pickelhaube helmets