Although first patented in 1904, radar wasn't useful militarily until when?

The correct answer is World War II because that is when radar technology was significantly refined and applied in military operations, making it a vital tool in air defense, naval warfare, and ground units. During this conflict, advancements in radar improved its range, accuracy, and ability to differentiate between friend or foe, which were crucial for detecting enemy aircraft and ships, particularly during critical battles such as the Battle of Britain and the Battle of the Atlantic.

Although radar was invented in 1904, its practical military applications were not realized until the developments in technology and tactics during World War II. In contrast, World War I saw only rudimentary uses of radio and some basic forms of detection, but nothing as sophisticated as radar. The Cold War era saw the continuation and enhancement of radar technology, but it was built upon the foundations laid during World War II. The Gulf War utilized advanced radar and targeting systems, but those capabilities were products of innovations from the earlier periods, especially the lessons learned during World War II.