Complex sentence: She conducted gunnery training off Cuba until 10 April, when she departed for Hampton Roads, Virginia, where she remained from 15 April to 15 May, when she went into the Norfolk Navy Yard for repairs, which lasted into early June.
Split into simpler sentences: She conducted gunnery training off Cuba until 10 April, when she departed for Hampton Roads, Virginia, where she remained from 15 April to 15 May. In mid-May, when she went into the Norfolk Navy Yard for repairs, which lasted into early June.