Complex sentence: Fairoaks was originally a private airstrip, opened in 1931, but was signed up for military use in 1936 becoming RAF Fairoaks during World War II, as a training airfield, and 6,000 pilots were trained there, mostly in Tiger Moths.
Split into simpler sentences: Fairoaks was originally a private airstrip, opened in 1931, but was signed up for military use in 1936. During World War II, as a training base, 6,000 pilots were trained there, mostly in Tiger Moths.