what a pantload of bogus hokum.
The MARINE CORPS was NEVER a part of the Army.
And Lt Pressley O'Bannon was a MARINE officer, not an Army officer.
http://www.montney.com/marine/brief.htm
"In 1834 the marines became part of the Department of the Navy."
Before that, it was governed by the Articles of War, meaning it was part of the Army.