As the Winter War began in 1939, Hallamaa and the SIGINT assets under his command were reorganized as the Signals Intelligence Office (). The Signals Intelligence Office was able to intercept Soviet messages and inform Colonel Hjalmar Siilasvuo of the enemy's movements during the Battle of Suomussalmi. With the intelligence, Colonel Siilasvuo had the initiative and could pocket and destroy the Soviet 44th Rifle Division at Raate road. The division had been en route to support the already encircled 163rd Rifle Division. For example, the Finns intercepted messages guiding the encircled Soviet troops how to light up signal fires for air supply pilots to recognize during night-time. Subsequently, the Finns lighted similar fires and some of the Soviet supplies landed on Finn-held ground. Over 20,000 Soviet troops were killed and military hardware in dire need, such as 43 tanks and 71 field guns, was captured. The decisive victory by the Finnish Army against superior enemy forces is cited as one of the most significant battles of the Winter War.