Special Forces Underwater Operations (SFUWO) is the term for United States Army Special Forces combat operations involving the use of underwater infiltration methods. These typically involve the use of closed circuit dive equipment to infiltrate a beach landing site (BLS) undetected.  The US Army Special Forces, also known as Green Berets have been conducting maritime operations and underwater operations since their founding in 1952. Currently, each company within a Special Forces Group mans, trains, equips, and deploys a SFUWO Operation Detachment Alpha (SFOD-A). These twelve-man teams train for SFUWO as their primary infiltration method when conducting one of their missions of unconventional warfare, direct action, counter-terrorism, foreign internal defense, among others.
US Army Special Forces first existed within the Office of Strategic Services (OSS) Operational Groups. Army Green Beret Combat Divers were first in the OSS Maritime Unit.  The Lambertsen Amphibious Respiratory Unit (LARU) was the first closed-circuit re-breather adopted by the US Military and used in Combat Operations with the OSS MU. It was invented by Dr. Christian Lambertsen.  Army Special Forces have been conducting these operations for nearly seventy years. It was the Army Special Forces that fielded the first true Special Operations Combat Divers with detachments conducting SFUWO in the early and mid 1950s, nearly a decade prior to the creation of the Navy SEALs. Archival footage from this time period depicts Green Berets conducting advanced underwater operations including underwater infiltration, submarine lockout procedures and even underwater demolition. 
The US Army Special Forces founded the Special Forces Underwater Operations School in Trumbo Point Annex, Naval Air Station Key West, in 1964.  Prior to that SF Detachment-Alphas were receiving disparate levels of dive training at their respective groups. SFUWO makes up C Company of the 2nd Battalion, 1st Special Warfare Training Group at the U.S. Army John F. Kennedy Special Warfare Center and School.
Army, Navy, Air Force, and Marine Corps personnel have previously attended the Combat Diver Qualification Course (CDQC), the seven week course that trains special operators to conduct SFUWO in a combat environment.  With a cadre of instructors primarily made up of Army Special Forces, along with a smaller number of Army Rangers, Navy SEALs, and Air Force pararescuemen and combat controllers, CDQC was formerly a standard part of the Air Force pararescue and combat control training pipelines (prior to the opening of the USAF Combat Diver Course in Panama City, FL), and both Tactical Air Control Party and Special Reconnaissance (formerly Special Operations Weather Teams) have also attended CDQC to become qualified in special warfare maritime operations.
The United States Navy Sea, Air, and Land (SEAL) Teams, commonly known as Navy SEALs, are the U.S. Navy's primary special operations force and a component of the Naval Special Warfare Command. Among the SEALs' main functions are conducting small-unit special operation missions in maritime, jungle, urban, arctic, mountainous, and desert environments. SEALs are typically ordered to capture or to kill high level targets, or to gather intelligence behind enemy lines. SEAL team personnel are hand selected, highly trained, and possess a high degree of proficiency in direct action (DA), and special reconnaissance (SR), among other tasks like sabotage, demolition, intelligence gathering, and hydro-graphic reconnaissance, training, and advising friendly militaries or other forces.
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, combatant diver, or combat swimmer. The word frogman first arose in the stage name The Fearless Frogman of Paul Boyton in the 1870s and later was claimed by John Spence, an enlisted member of the U.S. Navy and member of the OSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.
Underwater Demolition Teams (UDT), or frogmen, were amphibious units created by the United States Navy during World War II with specialized non-tactical missions. They were predecessors of the navy's current SEAL teams.
The United States Naval Special Warfare Command (USNSWC), also known as, is the naval component of United States Special Operations Command, the unified command responsible for overseeing and conducting the nation's special operations and missions.
The diver insignia are qualification badges of the uniformed services of the United States which are awarded to servicemen qualified as divers. Originally, the diver insignia was a cloth patch decoration worn by United States Navy divers in the upper-portion of the enlisted service uniform's left sleeve during the first part of World War II, when the rating insignia was worn on the right sleeve. When enlisted rating insignia were shifted to the left sleeve in late World War II, the patch shifted to the upper right sleeve. The diving patch was created during World War II, and became a breast insignia in the late 1960s.
The Naval Diving Unit (NDU), also referred to as the Naval Divers, is the special forces formation of the Republic of Singapore Navy (RSN) responsible for conducting special operations from sea, air, and land. The formation is made up of six squadrons, specialising in explosive ordnance disposal, underwater demolition, maritime security operations, and combatant craft operations.
A clearance diver was originally a specialist naval diver who used explosives underwater to remove obstructions to make harbours and shipping channels safe to navigate, but the term "clearance diver" was later used to include other naval underwater work. Units of clearance divers were first formed during and after World War II to clear ports and harbours in the Mediterranean and Northern Europe of unexploded ordnance and shipwrecks and booby traps laid by the Germans.
Underwater demolition refers to the deliberate destruction or neutralization of man-made or natural underwater obstacles, both for military and civilian purposes.
The Kopaska is the premier frogman and underwater demolition unit of the Indonesian Navy. The unit's motto is in Sanskrit: Tan Hana Wighna Tan Sirna. The unit's main duties are underwater demolition, destroying main underwater installations, reconnaissance, prisoner snatches, preparing beaches for larger naval amphibious operations, and counter-terrorism. During peacetime, the unit also deploys a team to serve as security personnel for VIPs and VVIPs. The personnel of Kopaska are recruited from Indonesian Navy seamen. Like other Indonesian special forces, Kopaska is trained to be able to conduct operations in the sea, including underwater, on land and airborne.
The Special Warfare Group (SWG) is the primary special forces unit of the Republic of Singapore Navy (RSN) responsible for conducting special operations from sea, air, and land. It is one of six squadrons of the Naval Diving Unit (NDU). It is also a component of the Special Operations Task Force (SOTF), alongside the Special Operations Force (SOF) of the Singapore Army. More information about the SWG is designated as classified.
Special Reconnaissance (SR)—formerly Special Operations Weather Technician or Team (SOWT)—is conducted by trained Air Force personnel assigned to Special Tactics Squadrons of the United States Air Force Special Operations Command who operate deep behind enemy lines to conduct covert direction of air and missile attacks, place remotely monitored sensors, and support other special operation units. Like other special operations units, SR units may also carry out direct action (DA) and unconventional warfare (UW), including guerrilla operations. As SOWTs they were tactical observer/forecasters with ground combat capabilities and fell under the Air Force Special Tactics within the Air Force Special Operations Command (AFSOC). The mission of a Special Operations Weather Technician was to deploy by the most feasible means available into combat and non-permissive environments to collect and interpret meteorological data and provide air and ground forces commanders with timely, accurate intelligence. They collect data, assist mission planning, generate accurate and mission-tailored target and route forecasts in support of global special operations, conduct special weather reconnaissance and train foreign national forces. SOWTs provided vital intelligence and deployed with joint air and ground forces in support of direct action, counter-terrorism, foreign internal defense, humanitarian assistance, special reconnaissance, austere airfield, and combat search and rescue.
Minedykkerkommandoen (MDK) or Norwegian Naval EOD Command is a clearance diver group. MDK is subordinate to the Royal Norwegian Navy. MDK is located at Haakonsvern Naval Base in Bergen and Ramsund Naval Base, in vicinity of Harstad.
Canadian Armed Forces (CAF) divers are specialists trained to conduct underwater operations within their respective environmental commands. Divers within the CAF are qualified into sub-categories of diving. Be it a member of a diving team or a CAF member who is maintaining currency and qualification through casual diving. Divers within the CAF are trained as Clearance Divers, Search and Rescue Technicians (SAR), Port Inspection Divers (PID), Ship's Team Divers, and Combat Divers.
The US employs divers in several branches of the armed forces, including the navy, army, marines, air force and coast guard.
Combat Rescue Officer (CRO) is a Special Warfare Officer career field in the United States Air Force. Its Air Force Specialty Code (AFSC) is 19ZXC and it was created to strengthen USAF Special Warfare personnel recovery capabilities by providing commissioned officer leadership that possessed an operational skillset paralleling that of the enlisted pararescuemen (PJ). The CRO specialty includes direct combatant command and control of Combat Search and Rescue (CSAR) operations. They plan, manage and execute the six tasks of CSAR: prepare, report, locate, support, recover, and reintegrate isolated personnel and materiel. CROs conduct strategic, operational and tactical level planning, provide battle staff expertise, manage theater personnel recovery operations and conduct combat special operations.
Army engineer divers are members of national armies who are trained to undertake reconnaissance, demolition, and salvage tasks underwater. These divers have similar skills and qualifications as professional divers. In the United States Army, they are members of the Corps of Engineers. In the British Army they may be Royal Engineer Divers or Commando Engineer Divers.
The Pasukan Khas Laut, commonly abbreviated to PASKAL, is the principal special operations force of the Royal Malaysian Navy.
The United States Air Force Combat Diver Course—administratively known as the 350th Battlefield Airmen Training Squadron, Det 2—is held at the Navy Diving Salvage and Training Center, Naval Support Activity Panama City and trains Pararescuemen, Combat Rescue Officers, Combat Controllers, and Special Tactics Officers to conduct and participate in special operations diving missions.
The Special Forces and Elite Forces include both a specially and higher trained unit and a small percentage of personnel from a specific Malaysian military branch, law enforcement or government agency. In Malaysia, the term 'Special Forces' is widely used by uniformed services for special forces, special operations forces and 'special' trained units while 'Elite Forces' for units that more trained and capable combat. Regular personnel must undertake specialized and higher training to be able to join the units of the 'Special and Elite Forces'. These 'Special and Elite Forces' are denoted by different beret colours, shoulder tabs, unit patches, skill badges and uniforms.