Nazi-Germany attacks the Sovietunion on June 22nd.
For national defence purposes Switzerland spends from 1939 to 1945 a total of 11.2 billion CHF (at today's value more than 100 billion), which amount to between 55% (1939) and 80% (1940/41) of the federal budget.
Switzerland introduces - for the first time in its history - a Federal Income Tax ("Wehrsteuer"), at that time primarily to finance the national defence effort.
Japan attacks Pearl Harbour in Hawaii. On December 7th, the United States enter WW2.