Final answer:
Winston Churchill, as the First Lord of the Admiralty in 1911, was the individual who urged the UK fleet to switch to oil, to improve naval efficiency and performance.
Step-by-step explanation:
The individual who first urged the UK fleet to switch to oil was Winston Churchill, who at the time was First Lord of the Admiralty before World War I. The year was 1911 when Churchill made this strategic decision to transition the Royal Navy from coal-powered ships to oil-powered vessels. This move was based on the superior performance characteristics of oil, such as greater efficiency and faster refueling times. It also coincided with Britain's geostrategic interests and the growing importance of oil as a global commodity, especially considering the vast oil reserves in the Middle East, which included the oil discovered in Iran in 1908 that was controlled by the Anglo-Persian Oil Company (later known as BP).