The case of Finland is a highly peculiar one, for they fought actively against the Soviets during the Winter War with some measure of success, then again from '41 to '44 during the Continuation War with less success and more German backing, and then from '44 to '45 engaged in the Lapland War with Germany while scaling down military operations to fulfill the requirements of the Moscow Armistice. In case you couldn't tell, Finland is one of the participants in the war I am most interested in.
The case of Finland is a highly peculiar one, for they fought actively against the Soviets during the Winter War with some measure of success, The Russian army was in terrible shape considering its size. Stalin caused that with his purges of officers and others. This was one of the reasons that hitler invaded the soviet union.
Here's an article about the Winter War, in a somewhat unusual language! History House: Those Burly Finns
And indeed some info on the Mannerheim Line showing pictures of the fortifications Mannerheim Line - Finnish fortifications of Winter War period