Final answer:
The first extensive use of jet aircraft and helicopters occurred during World War I, which was the first global conflict and brought about major changes in warfare.
Step-by-step explanation:
The first extensive use of jet aircraft and helicopters occurred during World War I. This war, which lasted from 1914-1918, was the first global conflict and brought about major changes in warfare. It introduced new technologies, including jet fighters and helicopters, which had a significant impact on the way battles were fought. These advancements in aviation paved the way for future developments in military aircraft.