Complex sentence: Leaving Milford Haven, Wales, on 13 December with a convoy bound for Gibraltar, good progress was made until the morning of the 15th when at 9:10 a.m. a German U-boat torpedoed the merchant steamer "Bernard".
Split into simpler sentences: Leaving Milford Haven, Wales, on 13 December with a convoy bound for Gibraltar, good progress was made. On the morning of the 15 December at 9:10 a.m., a German U-boat torpedoed the merchant steamer "Bernard".