In the summer of 1926 the prototype R-3NL, named Proletariy (En:proletarian) and registered RR-SOV, piloted by Mikhail Gromov, assisted by mechanic Yevgeny Radzevich, flew a round Europe flight: Moscow - Königsberg - Berlin - Paris - Rome - Vienna - Prague - Warsaw - Moscow; After flying for about 120 kilometers , a coolant expansion tank suffered fatigue failures, spraying water around the cockpit.