PRAGUE (AP) — The Czech Republic’s government signed an agreement with the United States on Monday to acquire 24 U.S. F-35 fighter jets as part of a deal worth about 150 billion Czech koruna ($6.6 billion), the biggest single purchase for the Czech military.

Czech Defense Minister Jana Černochová and U.S. Ambassador Bijan Sabet signed a memorandum of understanding for the deal. The Czechs also signed a letter of offer and acceptance, the final step in completing a contract between the governments, the Czech Defense Ministry said.

“By signing this intergovernmental agreement, our country and also our army enter a new era,” Černochová said.

The Czech government approved the deal in September.

The first of the 24 fighter jets should be delivered in 2031, with the rest by 2035. The American aircraft will replace the 14 JAS-39 Gripen fighter jets from Sweden that are currently used by the Czech army.

The Czechs will pay almost $5 billion to the U.S. for the aircraft, training of pilots, ammunition and other costs, Černochová previously said. The remaining money will be used to finance an upgrade of the Caslav air force base in central Czech Republic, fuel and training of staff, she said.

“The F-35 is the only system that can help us succeed in the future’s battlegrounds, and that in the case of need, we’ll manage to effectively defend ourselves against aggression, together with our allies,” chief of the general staff Lt. Gen. Karel Rehka said.

The Czech ministry has been negotiating the deal with the U.S. for more than a year during Russia’s invasion of Ukraine.