There must be, or they wouldn't've kept us all on duty.

I will of course keep a guard on duty while you are here.

Harry had an idea that other agents would still be kept on duty.

They always kept a guard on duty, just in case.

He and other officials suggest that a person be kept on duty at all times a church or synagogue is open.

A few law enforcement agencies still keep them on active duty.

Only three of those were ever kept on active duty.

He was lucky they'd been able to keep him on active duty at all.

That left seven, and keeping three on constant duty would be impossible.

I told you we always keep flight crews on duty.