During a survey of the wreck of the Grunion, the Lost 52 Project spotted a Miller-Dunn Divinhood Style 3 helmet lodged in the superstructure alongside the foundation for the aft deck gun. The helmet had partially imploded as the boat sank. The Divinhood Style 3 was a shallow water helmet used for dives to less than 50 feet. I would imagine that it was used by the crew for minor routine repairs in remote ports where shore or tender support was not available. This is what the helmet looked like when new:

Being a shallow water helmet it was used without a suit, weight belt, or weighted shoes. It just rested on the diver's shoulders. The Navy purchased quite a few of these helmets in the years leading up to WWII, so they were in the stock system. But the question remains: where they routinely carried by our boats during the war as part of a normal Table of Allowances? 

Thanks for your help.