Complex sentence: At once, the situation became clear, as the Swedish oil tanker "Divina"--on passage from Purfleet and bound for Ipswich--came out of the darkness; the extra light indicated that she was carrying explosive material.
Split into simpler sentences: At once, the situation became clear; the Swedish oil tanker "Divina"--on passage from Purfleet and bound for Ipswich--came out of the darkness. The extra light indicated that she was carrying explosive material.