[1] On October 16, 1916, he was commissioned to the U.S. Public Health Service and served for six weeks at the Immigration Station, Ellis Island, New York.

From November 1916 to September 1918, he was Medical Officer on the United States Coast Guard Cutter (CSG) Seneca assigned to Cuban and European waters for 17 months until the ship was transferred to the U.S. Navy during World War I.

For the next decades, from 1921 until his retirement from active duty in 1950 he worked at the Hygienic Laboratory, remaining there through its administrative and name changes to the National Institutes of Health.

[4] While still doing research work on LCM in 1939, Armstrong was able, for the first time, to adapt and transmit a human strain of poliovirus (the rarer and less dangerous Lansing type 2 strain[5]) from monkeys to small rodents, first to the cotton rat (Sigmodon hispidus hispidus) and then to white mice.

This accomplishment was revolutionary as it made possible the study of many aspects of infection and immunity in humans that could scarcely have been carried out with monkeys.