During the Winter War reports were received from the front stating that the Soviets were using a very unusual weapon. So unlikely this weapon was considered to be that initially these reports were not believed. Finally a lieutenant was sent to investigate in the belief he could disprove the claims of such weapons being used by the Soviets. Instead, the lieutenant reported back of an incident that took place in the village of Impilahti on 15 February 1940:
[...]During the same bombing X were dropped from aircraft. At least three cases I have personally verified. The X cannot have been thrown by the [exploding] bombs from sides [=anywhere else], because the nearest bomb craters are at least 200m away and the holes through snow are totally vertical.[...]
The last recorded incident of the Soviets using this curious weapon took place in Kuhmo on 13 March 1940 at 10.58 am, just two minutes before the peace.
What was this curious weapon?