Complex sentence: The weather also grounded the "Luftwaffe" for the most part, but on the first day, the "Luftwaffe" did manage to put 500 aircraft into the air, more than had been achieved for a long time.
Split into simpler sentences: The weather also grounded the "Luftwaffe" for the most part. On the first day, the "Luftwaffe" did manage to put 500 aircraft into the air, more than had been achieved for a long time.