Who served as the Commandant of the Marine Corps for 39 years?

The answer is rooted in the historical significance and leadership of Archibald Henderson, who served as the Commandant of the Marine Corps from 1820 to 1859, a remarkable tenure of 39 years. His extended leadership period significantly shaped the Marine Corps, solidifying its role and identity within the United States military framework. Henderson was known for his visionary approach and efforts in expanding the Corps during a transformative time, including the establishment of a professional officer corps and promoting the importance of the Marine Corps' amphibious capabilities. His legacy includes numerous reforms and the introduction of a structured training program that has had lasting impacts on the Corps.

In contrast, the other figures listed had notable contributions to the Marine Corps but did not serve nearly as long in the role of Commandant. For instance, John A. Lejeune is often recognized for his influential leadership during World War I, David H. Berger is more contemporary and focused on modernization efforts, and Holland M. Smith was well-regarded for his command during World War II. Their legacies are crucial to understanding the Marine Corps' evolution, but Henderson's unprecedented 39-year command remains a unique and defining aspect of Marine Corps history.