Stof's Ju 88 Page
The noticable external differences are in the canopy, early A-5's sharing the A-1 canopy (later A-5's used the improved A-4 canopy), the engines - the distinctive bulges on the lower cowls of the A-4 were not present on the A-5, and the shape of the propeller blades.
The armament varied between units and versions aswell.
Will get back to you with more details when I get time to check up my info.
Linear Mode
