Odd Piece of WWI a/c equipment

[joegertler]

The recent thread on finding WWI period photos of aviation had me going through an old thick album I've had in the files for many years (decades?)
Most of the album photos appear to have been taken overseas, except for the last third, which were clearly taken in the U.S. upon returning home.There were two slips of paper inserted in the pages that were marked 258 Bombardment Squadron, and Chester Penn. Being careful not to make a hasty assumption, I am not certain if Chester Penn is the name of the album's original owner/compiler, or it is Chester, Pennsylvania? Or if Chester Penn could be a location in England?
There WAS a 258 Sqd RAF at the end of the war that was the aeroplane unit stationed at the RAFs field for airships. As the album contains 70 photos of a wide variety of Balloons and Airships, this is the likely unit. The aircraft photos are mostly of British aircraft, and the last part of the album has many U.S. aircraft at a couple of different U.S. bases, after he returned home... and of U.S. training aircraft such as JN4D and Martin Bombers and others.
Here is an unusual photo that caught my attention. Not sure what this piece of equipment is. First impression was some sort of parachute rig, but the attachment fittings to the pilot don't seem to support that? He'd have a heck of a time swinging from that simgle hook link at his belly..Any ideas?