Complex sentence: In the early-1970s, a light blue Shade 1550 short sleeve shirt or blouse and Shade 1549 dark blue trousers replaced these earlier duty uniform variants and the blue service dress uniform became the single form of service dress.
Split into simpler sentences: In the early-1970s, a light blue Shade 1550 short sleeve shirt or blouse and Shade 1549 dark blue trousers. The 1550/1549 uniform combination replaced earlier duty uniform variants and the blue service dress uniform became the single form of service dress.