United States Space Force in the context of "United States Department of Defense"

The United States Armed Forces are the military forces of the United States. U.S. federal law names six armed forces: the Army, Marine Corps, Navy, Air Force, Space Force, and Coast Guard. Since 1949, all of the armed forces, except the Coast Guard, have been permanently part of the United States Department of Defense, with the Space Force existing as a branch of the Air Force until 2019. They form six of the eight uniformed services of the United States.

From their inception during the American Revolutionary War, the Army and the Navy, and later the other services, have played a decisive role in the country's history. They helped forge a sense of national unity and identity through victories in the early-19th-century First and Second Barbary Wars. They played a critical role in the territorial evolution of the U.S., including the American Civil War. The National Security Act of 1947 created the Department of Defense or DoD, (after a short period being called the National Military Establishment) headed by the secretary of defense, superior to the service secretaries. It also created both the U.S. Air Force and National Security Council; in 1949, an amendment to the act merged the cabinet-level departments of the Army, Navy, and Air Force into the DoD.

The United States Department of the Air Force (DAF) is one of the three military departments within the Department of Defense of the United States of America. The Department of the Air Force was formed on September 18, 1947, per the National Security Act of 1947 (codified into Title 10 of the United States Code) and it is the military department within which the United States Air Force and the United States Space Force are organized.

The Department of the Air Force is headed by the secretary of the Air Force (SAF/OS), a civilian, who has the authority to conduct all of its affairs, subject to the authority, direction and control of the secretary of defense. The secretary of the Air Force's principal deputy is the under secretary of the Air Force (SAF/US). Their senior staff assistants in the Office of the Secretary of the Air Force are five assistant secretaries for acquisition, technology & logistics; financial management & comptroller; installations, environment & energy; manpower & reserve affairs; and space acquisition & integration and a general counsel. The highest-ranking military officers in the department, and senior military advisers to the secretary, are the chief of staff of the Air Force and chief of space operations.

The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where signal quality permits. It does not require the user to transmit any data, and operates independently of any telephone or Internet reception, though these technologies can enhance the usefulness of the GPS positioning information. It provides critical positioning capabilities to military, civil, and commercial users around the world. Although the United States government created, controls, and maintains the GPS system, it is freely accessible to anyone with a GPS receiver.

A space force is a military branch of a nation's armed forces that conducts military operations in outer space and space warfare. The world's first space force was the Russian Space Forces, established in 1992 as an independent military service. However, it lost its independence twice, first being absorbed into the Strategic Rocket Forces from 1997–2001 and 2001–2011, then it merged with the Russian Air Force to form the Russian Aerospace Forces in 2015, where it now exists as a sub-branch. As of 2025, there are two independent space forces: the United States Space Force and China's People's Liberation Army Aerospace Force.

Countries with smaller or developing space forces may combine their air and space forces under a single military branch, such as the Russian Aerospace Forces, Spanish Air and Space Force, French Air and Space Force, or Iranian Islamic Revolutionary Guard Corps Aerospace Force, or put them in an independent defense agency, such as the Indian Defence Space Agency. Countries with nascent military space capabilities usually organize them within their air forces.

The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian (0° longitude) maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle, and thus it differs slightly from the historical Greenwich Meridian. At the latitude of the Royal Observatory, Greenwich the difference is 102 metres (335 ft).

It is the reference meridian of the Global Positioning System (GPS) operated by the United States Space Force, and of WGS 84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).

The United States Public Health Service Commissioned Corps (USPHSCC; also referred to as the Commissioned Corps of the United States Public Health Service) is the uniformed service branch of the United States Public Health Service and one of the eight uniformed services of the United States (along with the Army, Navy, Marine Corps, Coast Guard, Air Force, Space Force, and NOAA Commissioned Officer Corps). The commissioned corps' primary mission is the protection, promotion, and advancement of health and safety of the general public.

Along with the NOAA Commissioned Officer Corps, the Public Health Service Commissioned Corps is one of two uniformed services that consist only of commissioned officers and has no enlisted or warrant officer ranks, although warrant officers have been authorized for use within the service. Officers of the commissioned corps are classified as noncombatants, unless directed to serve as part of the military by the president or detailed to a service branch of the military. Members of the commissioned corps wear uniforms modeled after the United States Navy and the United States Coast Guard, with special Public Health Service Commissioned Corps insignia, and hold naval ranks equivalent to officers of the Navy and Coast Guard, along with corresponding in-service medical titles. Commissioned corps officers typically receive their commissions through the commissioned corps's direct commissioning program.

In the United States Navy, United States Coast Guard, United States Public Health Service Commissioned Corps (USPHS Corps), and National Oceanic and Atmospheric Administration Commissioned Officer Corps (NOAA Corps), captain is the senior-most commissioned officer rank below that of flag officer (i.e., admirals). The equivalent rank is colonel in the United States Army, Air Force, Space Force, and Marine Corps.

Reflecting its nautical heritage, the term captain is used as a military title by officers of more junior rank who command a commissioned vessel of the Navy, Coast Guard, or National Oceanic and Atmospheric Administration (NOAA) of patrol boat size or greater. Officers below O-6 who command aviation squadrons (typically O-5 commanders) usually use the less formal title "skipper".