Why did diesel engines become important for submarines during World War I?

During World War I, the diesel engine became the standard power plant for submarines because it offered significant advantages over the gasoline engines used in earlier designs.12

The primary reasons for its importance included:

• Safety: Unlike gasoline, which is highly volatile, diesel fuel is less volatile, making it much safer to store and handle within the cramped, confined spaces of a submarine.2
• Efficiency and Reliability: Diesel engines proved to be highly economical in their fuel consumption and demonstrated superior reliability under the demanding conditions of wartime operations.2
• Operational Standard: By the time of the war, the submarine had evolved into a craft that utilized diesel engines for surface propulsion and battery-powered electric motors for underwater travel, a configuration that balanced range, endurance, and tactical capability.1

While most World War I-era submarines relied on this diesel-electric combination, some specialized vessels, such as the British K-class, utilized steam turbines to achieve the higher speeds necessary for scouting roles.3