Complex sentence: From 1953 onwards, the first three prototype aircraft were hand-built at Salmesbury, these aircraft had been assigned the aircraft serials "WG760", "WG763", and "WG765".
Split into simpler sentences: From 1953 onwards, the first three prototype aircraft were hand-built at Salmesbury. These aircraft had been assigned the aircraft serials "WG760", "WG763", and "WG765".