In British voice procedure there were a number of appointment titles to be used to refer to or call someone by line or radio. For example, the commander was Sunray; the chief operations staff officer was Seagull - perhaps because the individual was always either squawking or sh....ng; Holdfast stood for Engineers; Sheldrake for gunners, Watchdog for military police; etc
In the bad, old days in a two troop battery with a separate battery command post, the command post officer (CPO), as opposed to the gun position officers in each troop, was Seagull. It was a fairly prestigious title, and one had to have one's act together to get the job. Okay, I'm prejudiced as I was the CPO C Battery in my second and third years of commissioned service.