Complex sentence: Royal Flying Corps officer Clive Gallop was built and running by December, and orders were taken for deliveries starting in June 1920; however, development took longer than estimated, and the first cars were not ready until September 1921.
Split into simpler sentences: Royal Flying Corps officer Clive Gallop was built and running by December. However, development took longer than estimated, and the first cars were not ready until September 1921.