The search for a second crew member is ongoing in Iran.

Combat search and rescue missions are complex and time-sensitive.

US air force elite units are trained for these missions and are often sent near conflict areas.

CSAR missions aim to find, aid, and rescue personnel in need, including downed pilots.

These missions happen in hostile environments, unlike conventional search-and-rescue efforts.

Sometimes, CSAR missions occur deep in enemy territory.

These missions are very time-sensitive because enemy forces are also trying to locate the US personnel.

CSAR missions are often done by helicopters with support from refuelling aircraft.

Verified video from Iran showed US military helicopters and a refuelling aircraft operating over Iran.

Airborne rescue missions have a long history, dating back to World War One.

The US military's pararescue units started with a 1943 mission in Burma.

The world's first helicopter rescue happened in 1944, and it was the first operational use of a helicopter in combat. This incident marked a significant milestone.

Formal search-and-rescue units were first established in the US after World War Two. However, modern CSAR began during the Vietnam War.

One mission, known as Bat 21, led to the loss of several aircraft and US casualties.

The Vietnam War required a vast expansion of CSAR missions with increased scope and complexity. This experience helped refine tactics and procedures.

The US Air Force has the primary responsibility for finding and rescuing military personnel.

This work is primarily done by pararescuemen, part of the military's special-operations community.

The official pararescue motto is 'These Things We Do, That Others May Live'.

Pararescuemen are highly trained as combatants and paramedics, with a very tough selection and training process.

The selection process takes about two years and includes parachute and dive training, as well as basic underwater demolition and survival training.

They also receive courses in battlefield medicine and complex recovery operations.

About 80% of potential pararescuemen do not complete the course.

On the ground, these teams are led by Combat Rescue Officers who plan and execute the recovery missions.

Pararescue teams were involved in thousands of missions in Iraq and Afghanistan.

In 2005, air force pararescue teams recovered a US Navy Seal who was wounded in an Afghan village.

Missions to recover downed US pilots have been rare in recent decades.

In 1999, a US pilot shot down over Serbia was recovered by pararescuemen.

In 1995, US pilot Scott O'Grady was rescued in a joint air force and Marine Corps CSAR mission after being shot down.

US elite teams continue to conduct combat rescue missions.

These missions are critical to the US military's operations.

The US military's pararescue units are highly trained and skilled.

Their work is essential to the success of US military operations.