active duty

Translations
действительная служба
He is currently on active duty in the military.
Он в настоящее время находится на действительной службе в армии.
Definitions
Active duty refers to a period of time when a member of the military is serving full-time in their official capacity, as opposed to being in reserve status or on leave. During active duty, service members are engaged in their military responsibilities and are subject to military law.
Words
active

adjective
действительная
duty

noun
служба