The two U.S. admirals who played a significant role in defeating the German U-boat offensive during World War I were Admiral William S. Sims and Admiral Ernest J. King. Admiral Sims advocated for improved anti-submarine tactics and coordinated efforts between the U.S. Navy and the British Royal Navy. Admiral King, later known for his command during World War II, also contributed to the strategic planning and implementation of anti-submarine warfare measures that were crucial in countering the U-boat threat. Their leadership and strategies helped turn the tide against the U-boat menace.