Complex sentence: On 20 April, the ship conducted its first gunnery practice, during which one of the ship's gunners, Coxswain John Johnson, was killed in an accident with one of the 5 inch guns.
Split into simpler sentences: On 20 April, the ship conducted its first gunnery practice. One of the ship's gunners, Coxswain John Johnson, was killed in an accident with one of the 5 inch guns.