What significant effect did World War II have on the Marine Corps in terms of expansion?

World War II had a profound impact on the size and structure of the Marine Corps, leading to a rapid increase in personnel. As the United States became deeply involved in the war, there was a tremendous demand for combat-ready troops. The Marine Corps expanded its manpower significantly to meet the needs of the war effort. Recruitment drives, including extensive advertising and outreach, attracted a large number of individuals wishing to serve.

By the end of the war, the Marine Corps had grown from about 75,000 personnel at the outset of the war to over 400,000. This expansion helped to establish the Marines as a vital force in amphibious warfare and solidified their role in military operations, leading to long-lasting changes in the Corps' structure and capabilities. The demand for forces during the war illustrated the role of the Marine Corps in major offensive operations, thereby justifying this significant expansion.