The Army of Czech Republic (ACR) has accepted into service 17 Russian-made Mil Mi-35 combat and 16 Mil Mi-171sh medium transport helicopters during a ceremony at its operational base in Perov on 9th of March 2006. The new helicopters with new supersonic and subsonic aircraft will be used to defend country and to meet commitment to NATO. The ACR took deliveries of the new helicopters in 2004-05 as partial repayment for a $3.5 billion debt Russia has owed the Czech Republic since the late 1980s. The Czech Ministry of Defence (MoD) is negotiating with Russia over the future modernization of the helicopters to NATO standards.