Opha May Johnson (ne Jacob, May 4, 1878 August 11, 1955) was the first woman known to have enlisted in the United States Marine Corps. She joined the Marine Corps Reserve on August 13, 1918, officially becoming the first female Marine.

The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through combined arms, implementing its own infantry, armor, artillery, aerial and special operations forces. The U.S. Marine Corps is one of the eight uniformed services of the United States.

The Marine Corps has been part of the U.S. Department of the Navy since 30 June 1834 with its sister service, the United States Navy. The USMC operates installations on land and aboard sea-going amphibious warfare ships around the world. Additionally, several of the Marines' tactical aviation squadrons, primarily Marine Fighter Attack squadrons, are also embedded in Navy carrier air wings and operate from the aircraft carriers.The history of the Marine Corps began when two battalions of Continental Marines were formed on 10 November 1775 in Philadelphia as a service branch of infantry troops capable of fighting both at sea and on shore. In the Pacific theater of World War II the Corps took the lead in a massive campaign of amphibious warfare, advancing from island to island. As of 2017, the USMC has around 182,000 active duty members and some 38,500 personnel in reserve.