Complex sentence: Both the RNAS and the RFC (and, after April 1918, the RAF) used the type as a trainer after its operational days were over, like the Pup, it proved a popular personal aircraft for senior officers.
Split into simpler sentences: Both the RNAS and the RFC (and, after April 1918, the RAF) used the type as a trainer after its operational days were over. Like the Pup, it proved a popular personal aircraft for senior officers.