Desertion

The Defector, by Octav Băncilă, 1906
Deserteur (Дезертир), by Ilya Repin, 1917
Armenian soldiers in 1919, with deserters as prisoners

Desertion is the abandonment of a military duty or post without permission (a pass, liberty or leave) and is done with the intention of not returning. This contrasts with unauthorized absence (UA) or absence without leave (AWOL /ˈwɒl/), which are temporary forms of absence.