(CNN) As Saudi Arabia, along with a growing list of other countries, cut diplomatic ties with Qatar on Monday, it called on its allies to cease all travel and transport with its neighbor.
One of Saudi Arabia biggest allies, however, is the United States, which also happens to maintain its biggest concentration of military personnel in the Middle East at Qatar's Al Udeid Air Base.
The sprawling base 20 miles southwest of the Qatari capital of Doha is home to some 11,000 US military personnel.
The base, which boasts one of the longest runways in the Persian Gulf at 12,500 feet, is a strategically important facility that can accommodate up to 120 aircraft.
In 2016, the base was used as staging ground to fly B-52 airstrikes against ISIS targets in Iraq and Syria. Early in the Afghanistan campaign, F-16 fighters and E-8C Joint Stars reconnaissance planes that monitor ground units were based there, along with refueling tankers.
According to a 2014 congressional research paper by Middle Eastern specialist, Christopher M. Blanchard, Qatar invested over $1 billion to construct the air base during the 1990s, despite having only a small air force of its own at the time. This in turn, "facilitated gradually deeper cooperation with US military forces."
The base houses the forward headquarters of the US Air Force Central Command, Combined Air and Space Operations Center and the 379th Air Expedition Wing.
The Combined Air and Space Operations Center (CAOC) oversees US military air power in Afghanistan, Syria, Iraq and 18 other nations, according to the Air Force.
Manned by personnel from the US Air Force, Army, Navy and Marines as well as coalition partner countries, the CAOC is "the nerve center" of air campaigns across the region, according to the Air Force.
Construction of the $60 million CAOC facility, which the Air Force says "resembles the set of a futuristic movie," was completed in 2003. At that time the US moved the CAOC from Saudi Arabia's Prince Sultan Air Base, where since 1997 it had overseen operations during the war in Iraq.
The 379th Air Expedition Wing is "the largest, most diverse expeditionary wing" in the Air Force, according to the wing's website. It has more than 100 aircraft currently at the Qatar base, including combat planes like the B-1 bomber as well as planes for airlift, refueling and intelligence, the website says.
"Approximately every ten minutes, an aircraft is taking off or landing here -- this is not just during the duty-day -- it's 24/7," the wing's website says.