Ukrainian and U.S. soldiers prepare for Exercise Rapid Trident 2011. Rapid Trident, a multi-national airborne operation and field training exercise in support of Ukraine's annual program to achieve interoperability with NATO. ArmySept. 20 (UPI) -- The Rapid Trident 21 exercise to enhance interoperability between Ukraine, U.S. and NATO partners started Monday, with an opening ceremony at Central City Stadium near Yavoriv, Ukraine, and will run through Oct. 1. Gen. Vladyslav Klochkov, co-director of Rapid Trident 21 from the Ukrainian side, who spoke at the opening ceremony in Ukraine Monday said in a press release. Allied and partner service members from 15 nations kicked off the exercise Monday with the opening ceremony at Central City Stadium near Yavoriv, Ukraine.