In what year did the Marines come under the Department of the Navy?

The correct year when the Marines came under the Department of the Navy is 1834. This significant change established the organizational structure that continues to this day, wherein the U.S. Marine Corps operates as a component of the Navy, functioning under the Secretary of the Navy. The decision to place the Marines under the Department of the Navy allowed for better integration and coordination between the two branches, especially in naval operations and amphibious assaults.

The other years mentioned do not reflect this organizational change. For instance, 1820 and 1805 predate this alignment, while 1847 is associated with key military actions during the Mexican-American War rather than the administrative restructuring of the Corps. Understanding this historical context helps clarify the role and evolution of the Marine Corps within the broader scope of U.S. military operations.