What was a “bubblehead”?

“Bubblehead” was probably intended to be a derogatory nickname for submariners. The name comes from the “bubble” in the inclinometer used to maintain depth. Even though it may have been intended to be somewhat derogatory, most sub sailors wore the label with pride. It was far better than being a “zoomie” (Naval Aviation) or a “skimmer”, a surface sailor.