Who was the first Marine officer to command an Army division in combat?

The first Marine officer to command an Army division in combat was Major General John A. Lejeune. Lejeune is a pivotal figure in Marine Corps history, known for his leadership during World War I, particularly during the battles of Belleau Wood and Soissons. His ability to command an Army division showcases the versatility and capability of Marine Corps leadership at the time. Lejeune’s appointment to this position was particularly significant given the inter-service dynamics and the need for effective joint operations during the war. This historical context emphasizes the importance of his achievements, distinguishing him as a leader who transcended the traditional boundaries between the services.