Well, I have gone back into the Marine Corps to pick up another WOD. I happen to work with a retired Gunny and to be honest I did wonder why the marines picked this for a rank. Officially it is Gunnery Sergeant, gunny is just a nickname.

Gunny is a respected nick-name and standard address for senior US Marine Sergeants, Gunnery Sergeant. It is from the early days of the American Navy. Up until World War II, many warships utilized the contingent of marines on board to man their cannons to augment the regular crew. Thus, a senior enlisted Marine non-com, already skilled with the use of small arms and fighting on both land and at sea, became knowledgeable about sea and land-based artillery as well. He was usually adept at dispensing justice to soldiers and sailors alike, and understood the duties and tasks of both. Even today, with the deep and abiding rivalry that often runs between sailors and marines, and the social gap between officer and enlisted as well, they all pay close heed to what the 'gunny' has to say.

So in the Navy it would be “Listen to what Senior says.” In the Marines it is listen to what Gunny says.”