Complex sentence: En route to San Diego, the ship stopped in San Francisco (Treasure Island Naval Base) on 15 September for three days of shore leave; while there, Bucher received notice of his promotion to commander.
Split into simpler sentences: En route to San Diego, the ship stopped in San Francisco (Treasure Island Naval Base) on 15 September for three days of shore leave. While there, Bucher received notice of his promotion to commander.