Yes, U.S. planes were shot down by Russian planes during World War II, though these incidents were relatively rare and often stemmed from the complex relationship between the Soviet Union and the United States at the time. While the two nations were allies fighting against the Axis powers, they had very different strategic goals and were not always entirely cooperative, especially in the skies.
One of the most notable instances occurred when U.S. aircraft were operating in Soviet-controlled airspace. The Soviet Union, after signing the Lend-Lease Agreement with the United States, received vast quantities of military aid, including planes, trucks, and other supplies. However, despite being allies, the Soviet Union was extremely cautious about foreign aircraft operating in its airspace, and Soviet air forces sometimes misidentified U.S. planes as enemy craft.
A particularly famous incident involved B-17 Flying Fortress bombers. In 1944, a group of U.S. bombers on a mission to bomb German targets over Eastern Europe was attacked by Soviet P-39 Airacobra fighters. The Soviet pilots, having not been informed that American aircraft would be operating in their airspace, mistook the B-17s for German bombers. As a result, the Soviet pilots engaged in combat with the American planes, leading to several U.S. aircraft being shot down.
Additionally, there were cases of friendly fire incidents involving U.S. fighter planes and Soviet aircraft. These occurrences were often a result of miscommunication or misunderstanding, with Soviet pilots firing at U.S. planes that had strayed too close to Soviet positions or airfields.
Despite these incidents, the overall cooperation between the Soviet and U.S. forces outweighed such occurrences. The shared goal of defeating the Axis powers helped prevent these misunderstandings from escalating into more serious conflicts between the two nations during the war.