Complex sentence: Under state control, costs at Rolls-Royce were tightly controlled, and the company's efforts largely went into the original TriStar engines, which had needed considerable modifications between the L-1011's first flight and service entry.
Split into simpler sentences: Under state control, costs at Rolls-Royce were tightly controlled. The company's efforts largely went into the original TriStar engines, which needed considerable modifications between the L-1011's first flight and service entry.