The T669.0 series locomotive, nicknamed “Čmelák” (Bumblebee), was produced from 1963 by ČKD Prague. It is a heavy six-axle diesel locomotive designed mainly for shunting and freight transport. Powered by a K 6 S 310 DR engine with 993 kW output. More than 800 units were built and served in Czechoslovakia and other countries. It remains popular among railway enthusiasts.