Complex sentence: The third fighter unit to occupy RAF Andreas was No.93 Squadron RAF (93 Sqn) which had an entirely different background, previously having been involved in the development of night fighter tactics using Havocs equipped with radar and Turbinlite searchlights.
Split into simpler sentences: The third fighter unit to occupy RAF Andreas was 93 Squadron (93 Sqn) which had an entirely different background. During this period 93 Sqn had been involved in the development of night fighter tactics using Havocs equipped with radar and Turbinlite searchlights.