Complex sentence: The planned fuel stores amounted to 3,900 tons of oil and 2,500 tons of coal; at a speed of 14 kts, this would have enabled a maximum range of 8,000 nautical miles.
Split into simpler sentences: The planned fuel stores amounted to 3,900 tons of oil and 2,500 tons of coal. The ships had a planned cruising speed of 14 kts, and with full fuel stores, the ships would have had a maximum range of 8,000 nautical miles.