Your father was most likely on the German side on World War II participated.
From this generation and at that time hardly a male person and Latvian descent who emigrated from Latvia as a civilian, just to western countries. These men were all members of the Latvian Legion and prisoners of war of the Western Allies.
After their captivity, many were taken into the army of the British and the United States. In the following years many Latvian refugees emigrated from Germany to the United States and the countries of the Commonwealth.
I see only one way to find detailed information about your father and their ancestors, namely, a request to the Latvian State Historical Archives Archives in Riga / Latvia.
By the way, as you can see, my surname is also Avotins. My father was Latvian veteran on the German side. However, if we are related, I can not say yet. The surname is Avotins in Latvia, as often as elsewhere Smith or Mueller. Inside Riga telephone book can be find five pages with this name. The family name Avotins is a diminutive term ofa (water) source.