Complex sentence: The Germans retorted by pointing out that "Dronning Maud" had not been fully marked as a hospital ship, as she had retained her black hull instead of it being painted white with a horizontal green stripe.
Split into simpler sentences: The Germans retorted by pointing out that "Dronning Maud" had not been fully marked as a hospital ship. She had retained her black hull instead of it being painted white with a horizontal green stripe.