When I read "mine", I thought of anti-personnel landmines and was confused why you'd want to radio-trigger those.

These were demolition charges designed to destroy objects like bridges. According to https://www.quora.com/Is-it-true-that-the-Finnish-army-used-..., there were a total of 25 such mines hidden, with each containing hundreds to thousands of kilograms of explosives.

https://www.standingwellback.com/russian-ww2-radio-controlle... is also worth a read.