Complex sentence: The Stirling's low operational ceiling of just 12,000 ft--also caused by the thick wing--meant that it was usually picked on by night fighters; within five months, 67 of the 84 aircraft in service had been lost.
Split into simpler sentences: The Stirling's low operational ceiling of just 12,000 ft--also caused by the thick wing--meant that it was usually picked on by night fighters. And within five months, 67 of the 84 aircraft in service had been lost.