Complex sentence: In the early part of the War, he had been an aide to Major-General Hoskins in East Africa; after his transfer to the Middle East, he planned to become a pilot, but a foot injury prevented him from taking flying lessons.
Split into simpler sentences: In the early part of the War, he had been an aide to Major-General Hoskins in East Africa. After his transfer to the Middle East, he planned to become a pilot, but a foot injury prevented him from taking flying lessons.