Sentence:  If the acting captain wanted his acting lieutenant to sit on his ass around the station all night , Killpath would just have to go out and drag Gun back by the heels <WSD>once</WSD> an hour ; because he 'd be damned if he was going to be a mid-watch pencil-pusher just to please his ulcerated pro-tem captain . 
Meaning of the word marked with <WSD> tags:  on one occasion