The Base aérienne 172, originally named Fort-Lamy and later Sergent chef Adji Kosseï, is a French Air Force operational site located in N'Djaména, Chad. Established in 1939, it has served as a permanent detachment base for French Air Force aircraft from 1939 to 1975, and again from 1986 until its planned retrocession on January 30, 2025. During World War II, it was a crucial stop on the Allied air route between Takoradi, Ghana, and Cairo, Egypt. From 2014 to 2022, the base hosted the headquarters of Operation Barkhane, which involved 4,000 French soldiers operating across a vast region including Chad, Niger, Burkina Faso, Mauritania, and Mali. Since 1986, as part of Operation Épervier, the base has hosted a French Air Force group comprising over 300 airmen, operating various aircraft including Mirage 2000C RDI, Mirage F1 CR (until 2010), Transall C160, CASA CN 235, and C-135 refueling aircraft. The French forces at the base provided protection for French interests and nationals, logistical support (refueling, transport, training) to Chadian armed and security forces, and intelligence support. The base is located northwest of N'Djamena International Airport. Following the denunciation of military cooperation agreements by the Chadian president in November 2024, the French military presence, including three Mirage 2000 aircraft, began withdrawing in December 2024, with the base officially retroceded on January 30, 2025.