In 1864, during the American Civil War, he joined the Union Army by enlisting in the 34th Iowa Infantry Regiment, serving until being mustered out with the unit in August 1865.

Back in Japan he initially was a teacher and surveyor for a school of the Hokkaido Colonization Office, during which time he introduced and taught methods of triangulation to survey large areas.

[3] During the Taiwan Expedition of 1874 Wasson, who just had been commissioned as a colonel of engineers in the Imperial Japanese Army, accompanied General Saigō Tsugumichi as his chief of staff.

He could no longer support the lifestyle which he had come accustomed while working in Japan and amassed gambling debts, eventually embezzling $24,000 by faking a robbery.

Beside service in the Iowa National Guard Wasson, now in his 50s, joined the US Army for a third time; enlisting for the Spanish–American War.

[13] Wasson worked and lived in various places and businesses, from mining in Mexico to engineering along the east coast.