In response to the increasingly tense situation in the Ukraine, the U.S. Air Force augmented the four F-15C Eagles rotated to Šiauliai International Airport, Lithuania, with six additional F-15Cs. The 10 Eagles are part of NATO-led Baltic Air Policing, a quick reaction alert mission that guards the airspace over the three Baltic states of Estonia, Lithuania, and Latvia. Regular training events test the interoperability and readiness of partner air forces involved in Baltic Air Policing, which sees rotations of units from different NATO nations. The U.S. Air Force is responsible for the current rotation, originally scheduled to last until May 1, at which point a rotation composed of Polish Air Force MiG-29A, British Royal Air Force Typhoon, and Danish Royal Air Force F-16AM aircraft are due to take over. On April 1, U.S. Air Force F-15Cs scrambled as part of that training.