Complex sentence: The "Luftwaffe" was busy replacing its losses from the Western campaign in which it had lost 28 per cent of its aircraft destroyed, but it could still command over one thousand medium bombers by July 1940.
Split into simpler sentences: The "Luftwaffe" was busy replacing its losses from the Western campaign in which it had lost 28 per cent of its aircraft destroyed. But it could still command over one thousand medium bombers in July 1940.