During WWII when the UK needed to build a lot of ships, they chose to build coal-burning ships because the UK knew that it could always get enough coal to fuel

During WWII when the UK needed to build a lot of ships, they chose to build coal-burning ships because the UK knew that it could always get enough coal to fuel ships whereas they weren't certain about getting enough oil. Warships need to be able to go fast, so all of the Royal Navy's ships had been switched to oil long ago (because oil-fueled ships go about twice as fast) and that never changed during the war, but the thousands of "merchant" ships they built (and asked the US to build for them) ran on coal.