From what I can tell, in both the Winter war and Continuation war the Red Army took massive casualties despite outnumbering Finnish Forces many time over. Why? Did the Finnish have better equipment or training? Did the Soviets underestimate them? Any information is appreciated.
This has actually been asked before so if you are looking for a more in-depth discussion, I suggest that you do a search. From my knowledge of the topic, there were a number of reasons:
The Soviets were not sufficiently prepared and did indeed underestimate the Finns. The Finns themselves were actually quite prepared for the invasion and had their own defensive line (the Mannerheim Line). Unlike, say the Baltic states, the Finns were fully committed to fighting. The Soviets invaded with little preparation. For example, in some cases the junior officers didn't even have accurate maps of the region, or the Finnish defenses would be absent on their maps. They received their orders, and those orders didn't take into account the existence of Finnish bunkers. The officers didn't have sufficient instructions or training about what to do in situations they weren't even expecting in the first place. Needless to say, the outcome was disastrous for many Soviet units.
The Red Army in general wasn't in good shape. While the impact of the purges of late 1930's is sometimes overstated on the defeats at the outset of the German invasion, in 1939 the effect of the purges was quite palpable. Officer training and experience was poor, especially when it came to besieging Finnish defenses.
The terrain was highly favorable to the Finns. The Karelian isthmus, is narrow, kind of like a bottleneck. Furthermore, much of it was covered in forests, lakes, swaps, rivers etc. Thus Soviet advantages in numbers and vehicle was hard to take advantage off. The Finns were quite good at setting up ambushes along narrow forest roads. The exceptionally cold winter weather didn't help either.
Over the course of the war, however, the Soviets were able to regroup, change their leadership, learn from their mistakes and change their tactics. They brought in more troops and heavy artillery, and just brute forced their way through the Finnish defenses.
How was the situation in Finland for the Soviet Union similar to or different than other guerilla style conflicts in history like the Vietnam War or the Soviet invasion of Afghanistan?
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