Awsome pic - Bravo Zulu!
My dad said they slept in hammocks at Great Lakes in 1942, but theirs were strung extremely taut between steel pipes -- not at all loose like we do. He spent the war on a sub chaser in the Pacific but they didn't have hammocks aboard. More's the pity. I recall seeing, somewhere, a pic of hammocks hung in a 19th century British ship. IIRC, those had spreader bars at each end.
Edit: If you Google "HMS Victory hammock pictures" some of the links will show hammocks on Lord Nelson's flagship. I didn't see any spreader bars there. OTOH, this pic on the newer HMS Belfast shows one in use, with a detachable spreader bar -- shades of the bridge hammock!