Sergei Biriuzov Quote

The storming of the Mannerheim Line was regarded as a model of operational and tactical art. Troops were taught to overcome the enemy's protracted defense by a gradual accumulation of forces and a patient "gnawing through" of breaches in the enemy's fortifications in accordance with all the rules of engineering science. Insufficient attention was paid to questions of co-operation among different branches and services of the armed forces under rapidly changing conditions. We had to retrain ourselves under enemy fire, paying a high price for the experience and knowledge without which we could not beat Hitler's army.

Quoted in "The Winter War: The Soviet Attack on Finland" - Page 146 - by Eloise Engle, Eloise Paananen, Lauri Paananen - History