Complex sentence: The Type O was the largest aircraft that had been built in the UK and one of the largest in the world and most were built in two versions, the Handley Page O/100 (H.P.11) and Handley Page O/400 (H.P.12).
Split into simpler sentences: The Type O was the largest aircraft that had been built in the UK and one of the largest in the world. Most were built in two versions, the Handley Page O/100 (H.P.11) and Handley Page O/400 (H.P.12).