Did you know that terms people use to describe the services collectively aren't interchangeable? For instance, "the military services" and "the armed forces" don’t mean the same thing.

Here's a quick guide to the various terms:

Military Services

Soldiers assigned to Alpha Battery, 4th Battalion, 319th Airborne Field Artillery Regiment, fire a M119 105 mm howitzer during exercise Dynamic Front 19 at Torun, Poland, March 5, 2019.
Photo By: Army Spc. Rolyn Kropf

The military services are all part of the Defense Department.

Marines with Special Purpose Marine Air-Ground Task Force Crisis Response Africa 19.1 conduct a helicopter support team training event with a Marine Corps MV-22 Osprey at Morón Air Base, Spain, March 13, 2019.
Photo By: Marine Corps Sgt. Katelyn Hunter

Just three of the military services are departments: The Department of the Army, the Department of the Navy and the Department of the Air Force. The Marine Corps falls under the Department of the Navy.

A special tactics airman with the 26th Special Tactics Squadron looks onto an F-35A Lightning II fighter aircraft at Cannon Air Force Base, N.M., Feb. 26, 2019. Photo By: Air Force Staff Sgt. Rose Gudex

Armed Forces

There are five armed forces: The four military services plus the Coast Guard.

The Coast Guard Cutter Robert Ward is escorted by San Francisco and Sacramento Coast Guard assets as the crew journeys to Coast Guard Sector San Francisco on Yerba Buena Island for a ceremonial commissioning, Feb. 22, 2019. The Robert Ward was the second fast response cutter to be stationed in California and will provide vital capabilities to the Coast Guard in ensuring the safety and security of California’s shipping ports. Photo By: Coast Guard Petty Officer 3rd Class Jordan Akiyama

The Coast Guard is not administered by the DOD. Instead, it is part of the Department of Homeland Security.

During wartime, the president or Congress may direct that the Coast Guard operate as part of the Navy. During peacetime, the Coast Guard and the Navy often coordinate their activities.

Uniformed Services

There are seven uniformed services: The five armed forces plus the Public Health Service Commissioned Corps, which falls under the Department of Health and Human Services, and the National Oceanic and Atmospheric Administration Officer Corps, which falls under the Commerce Department.

Officers in the PHS Corps and NOAA Corps wear Navy uniforms and use Navy ranks. There are no enlisted or warrant personnel in these services.

Army Reservists and National Guardsmen dentists and dental assistants work alongside a U.S. Public Health Service personnel in Pharr, Texas during a free dental clinic as part of Operation Lone Star, an annual medical disaster preparedness exercise, July 27, 2016. Photo By: Texas Army National Guard Sgt. 1st Class Malcolm McClendon

The U.S. surgeon general, a vice admiral, directs the PHS Corps, which provides licensed medical and health sciences professionals to the PHS, DHHS, other uniformed services and other government agencies.

The NOAA Corps is made up of technically skilled science officers who can be incorporated into the armed forces in wartime. In peacetime, the corps supports defense requirements in addition to its purely nonmilitary scientific projects at sea, in the air and in laboratories.

Federal Service Academies

• The U.S. Military Academy in West Point, New York
• The U.S. Naval Academy in Annapolis, Maryland
• The U.S. Air Force Academy in Colorado Springs, Colorado
• The U.S. Coast Guard Academy in New London, Connecticut
• The U.S. Merchant Marine Academy in Kings Point, New York

What's the Merchant Marine?

The Merchant Marine is made up of civilian mariners and merchant vessels engaged in commerce or transportation of goods and services in and out of the navigable waters of the United States.

Supplies are delivered to the amphibious assault ship USS Kearsarge as part of a replenishment at sea during an exercise in the Atlantic Ocean, Aug. 30, 2018. Photo By: Marine Corps Cpl. Aaron Henson

While the Merchant Marine isn’t a government agency or military service, in wartime it can become a Navy auxiliary service to deliver military personnel and materiel. The Navy also maintains a Department of Naval Science at the Merchant Marine Academy.

Merchant Marine Academy graduates are required to spend eight years as a commissioned officer in the reserve or National Guard component of any branch of the armed forces.