Complex sentence: Shortly after he joined the Royal Navy, he volunteered to become a member of the British Arctic Air Route Expedition (BAARE) led by Gino Watkins as he expedition doctor and to be in charge of the expedition's sled dogs.
Split into simpler sentences: Shortly after he joined the Royal Navy, he volunteered to become a member of the British Arctic Air Route Expedition (BAARE) led by Gino Watkins. He took part as the expedition doctor and to be in charge of the expedition's sled dogs.