Complex sentence: Between 1957 and 1958 the first batch had the wing slats removed and were redesignated Sabre Mk 31 and were supplemented by 20 new-build aircraft.
Split into simpler sentences: Between 1957 and 1958 this batch had the wing slats removed and were redesignated Sabre Mk 31. These Sabres were supplemented by 20 new-build aircraft.