Complex sentence: In 1967, the Puma was selected by the Royal Air Force (RAF), having been impressed by the Puma's performance, it was given the designation "Puma HC Mk 1".
Split into simpler sentences: In 1967, the Puma was selected by the Royal Air Force (RAF). They having been impressed by the Puma's performance, it was given the designation "Puma HC Mk 1".