Simplify the following text for a Grade 9 native English-speaking person.
Original: From July 1940 coastal shipping convoys and shipping centres , such as Portsmouth , were the main targets ; one month later the Luftwaffe shifted its attacks to RAF airfields and infrastructure .
Simplified: From July 1940 coastal shipping convoys and shipping centres , such as Portsmouth , were the main targets . A month later the Luftwaffe shifted its attacks to RAF airfields and infrastructure ( other useful war targets ) .