Desertion is the abandonment of a military duty or post without permission and is done with the intention of not returning. This contrasts with unauthorized absence (UA) or absence without leave, which are temporary forms of absence.
The Defector, by Octav Băncilă, 1906
Deserteur (Дезертир), by Ilya Repin, 1917
Armenian soldiers in 1919, with deserters as prisoners
A 1918 cartoon by Cecil Hartt making light of the high incidence of soldiers going absent without leave in the Australian Imperial Force
Military service is service by an individual or group in an army or other militia, air forces, and naval forces, whether as a chosen job (volunteer) or as a result of an involuntary draft (conscription).
Military service in Spain (1945)
Timetable of military duties, Switzerland