Complex sentence: The ship went into drydock on 21 June and remained there until 8 December; and, after she was refloated, work renewing the ship continued into the spring of 1976.
Split into simpler sentences: The ship went into drydock on 21 June. She remained in drydock until 8 December; and, after she was refloated, work renewing the ship continued into the spring of 1976.