In a round-the-clock exercise, several Su-35 aircraft practiced various tasks including short takeoffs and landings, two-jet combat, four-jet combat and aerial refueling. After nearly two years of adaptation and training, the People's Liberation Army Air Force has improved its combat capacity with the Su-35 fighter jets from Russia. China confirmed a 2-billion-U.S.-dollar deal to buy Su-35 fighter jets from Russia in Nov. 2015, and the first batch of four jets was delivered in Dec. 2016.