I'm afraid I'm not going to be of much help as far as telling you what the specific straps/slings were for, but I'm all twitterpated to see them. I'm from Newaygo, Mi where the robey tackle company was located back in the 40's. It is kind of a big part of the history of our small town how the local women who worked at the tackle company were able to pitch in and be part of the war effort. If you do a google search on "robey gals" you'll pull up some articles and interviews about it. To that end, i'm working on putting together a collection/display of robey products and would love to purchase anything with the robey lable on it that's available. would welcome any pm's from anybody with any robey stuff for sale. thanks.
~dave