The second youngest of eight children on a farm that couldn't support such a big family from crops alone, he took to hunting from a young age.
When he joined the White Guard at age 17 he already was a good marksman and soon began winning local competitions with a variety of weapons, both individually and in groups.
During his conscription service 1925-1927 in Bicycle Battallion 2 he was promoted to NCO. He got his sniper education in rehersal training 1938.
Dressed for the cold.
The Winter War 30 Nov 1939 to 13 Mar 1940 saw squad leader Häyhä soon gained reputation as a master sniper with 240 to 540 confirmed kills by the end of the war, depending on the source cited. He made good use of his experience in hunting when searching for good sniper nests and laying still in them waiting for targets whole days. Some days it was close to -40oC (-40oF) but Simo knew well how to dress for cold weather.
A hollow-point expanding bullet.
After 98 days of fighting Häyhä was wounded in the face by expanding bullets used illegally by the Russians. They had been banned from wartime use by the Hague Convention 1899. His wounds were so bad rumours of his death soon started to circulate. Even newspapers reported him dead and Simo, who had spotted the news in the papers, had to write to his brother "Stop the funeral, the deceased is missing." His recovery took several years and 26 surgical operations.
He continued farming and hunting after the war. He was also a renowned hunting dog breeder.