Final answer:
The UK switched its naval fleet to oil in the early 20th century due to the increasing importance of oil and the discovery of large reserves in the Middle East.
Step-by-step explanation:
In the early 20th century, the United Kingdom switched its naval fleet to oil. This change was driven by a combination of factors, including the increasing importance of oil as a commodity and the discovery of large oil reserves in the Middle East. The Anglo-Persian Oil Company (now known as BP) was established in 1908 to control oil production in Iran. Additionally, the British-controlled multinational, TPC, received a concession to develop Iraq's oil.