Complex sentence: At 10:54 "Dublin" saw the track of a torpedo passing ahead of her, at 11:12 a submarine was sighted, and at 11:15 another one was spotted, which fired two torpedoes at her.
Split into simpler sentences: At 10:54 "Dublin" saw the track of a torpedo passing ahead of her. At 11:12 a submarine was sighted and at 11:15 another one was spotted, which fired two torpedoes at her.