Complex sentence: After a period of neutrality, Italy entered World War II on 10 June 1940 alongside Germany, in which the Royal Air Force could deploy more than 3,000 aircrafts, even if less than 60% were serviceable.
Split into simpler sentences: After a period of neutrality, Italy entered World War II on 10 June 1940 alongside Germany. The Royal Air Force could deploy more than 3,000 aircraft, although less than 60% were serviceable.