The deadlights do appear to be located mostly to the sides of crew stations, but in the very limited space an open cover, swinging with the movement of the boat, or even stationary, would be a hazard.  Other lock-back mechanisms, such as a wire, not visible under the concretion are possible.  The only function of the deadlights would be to allow light into the cabin.  They would not be useful and as mentioned above would be dangerous for night-time operations, but even if they were used only for daytime maintenance swinging covers would be hazardous in the cramped cabin.  Perhaps the covers were added later to make the boat more stealthy or in response to leaks and left in the closed position.  Still it seems some other solution would have be used rather than these complex devices if they were never opened.

     I had originally used pyramidal deadlight glasses in my construction. Found in many nautical installations, these would have provided more light in the cabin.  The Hunley deadlights appear to be simple flat glasses, less than half an inch thick.

     The hatch lids also have deadlights.  These may also be covered, but published x-rays don't show the large, hinged covers revealed in the cabin.  Similarly, an x-ray of one of the hatch ports reveals a mounting ring and rivets or bolts but nothing else.