When the Red Army crossed the border into Finland in 1939, along with them came a battalion of remote-controlled tanks, controlled by another tank some 1000 meters behind them. Along with the usual heavy armaments, the tank drones shot fire from flamethrowers, smoke grenades, and some were even dropping ticking time bombs, just waiting to get close to their target.
It's a surprising technological feat for a country that had only just recently undergone a wave of modernization.
The Soviets had this remote technology in its pocket for a decade, having first tested the tanks on a Soviet T-18 in the early 1930s. While the earliest models were controlled with a very long wire, the USSR was soon able to upgrade to a more combat-friendly radio remote. By the time the Nazis invaded the Soviet Union in June 1941, the Red Army had two battalions of the drones, which it called teletanks. At this time, the teletank technology was in Soviet T-26 tanks, called the Titan TT-26, and there was a big list of tanks, ships, and aircraft on which the Soviets wanted to equip with tele-tech.
Unfortunately, the TT-26 wasn't able to fully participate in the Soviet Union's Great Patriotic War. In the beginning of Operation Barbarossa, Hitler's Luftwaffe was able to destroy the vast majority of the Red Army's TT-26 teletanks. In the months that followed, it proved to be more economical and timely to produce a regular version of the T-26 and man them with human crews.
T-20 Komsomolets Teletanks
It would have been unlikely that the teletank technology would have made the difference on the Eastern Front of World War II anyway. They were notoriously unreliable in unfamiliar terrain and were easily stopped by tank spikes. If a teletank managed to outpace the range of its controller, it simply stopped and did nothing. The Soviets mitigated this by mining the hatches of the tanks, but an inoperative tank is still not very useful to the Allied cause.
Eventually, the USSR's remaining teletanks were converted to conventional tanks in order to join the fight against the Nazis. Perhaps the emerging technology of the time was an interesting aside for military planners before the war, but the fun and games must stop when you have to start fighting for survival.