It's a broom, though not mounted correctly. On Wahoo, and later on other boats, it was normally tied to the periscope, to show the boat had swept the seas of enemy ships (No torpedoes left).
On Cobia they have welded a socket, to mount the broom, on the shears. I have several photos clearly showing it. Email me at << mkeatingss(at)cox.net >> if you want a copies.
As a side note, Periscope Film.com, may soon be releasing a couple of new books. These are; "The Submarine" ( Navpers 10490 - "Basic Enlisted Submarine Text Part 1") and "Standard Submarine Phraseology" (Originally issued by Sublant).
If these prove a popular (good sales), Navpers 16162 - "Submarine Electrical Installations", 16164 - "Submarine Air Systems" and 16166 - "Trim and Drain Systems", could be released at a future date.
Mike K.