I bought these items way back in the early 1980s. They're the ONLY ones I've ever seen. The top one shows the obverse side, the bottom one shows the reverse.
Made by "Irvin Air Corporation" (pre "Irvin GQ Parachutes"), they're labelled as "Extension Strop CSPEP" (Container Straps Personal Equipment Parachutist). It's dated as issued 14-Nov-1962. They're obviously for the CSPEP Mk1 because that's around the time that (I believe) the CSPEP replaced the Personal Weapons Container (correct name?); the fabric and stitching is identical to that on the CSPEP Mk1, and; the next mark of the CSPEP was already in service by the mid/late 1980s.
I initially thought they'd extend one of the closing straps - but that didn't seem to work. I then thought they might be early "Accessory Straps" (IE: "Weapon Straps" - but that didn't work, either. Are there any old sweats who know what were these things used for?
When I was in service, we used the CSPEP Mk 2. When I worked odd days in company stores, I saw only jump kit that I was familiar with - never these. I'm thinking that that were a short-lived item.
The ONLY thing I can imagine they did was link two parallel straps to each other. In a Irvin GQ advert, I saw a pic of a Paratrooper with a CSPEP Mk1 and there was a strap (I'll call it a "link strap") doing this - but it didn't seem to look like these things. I'll try to find the advert and post it here.
The advert showed the straps (vertical AND horizontal) being used in parallel; on my wings course, I was taught to cross the straps at least one pair of straps. Crossing the straps meant that they were more secure and, obviously, there was no need for a link strap.
In the meantime, I invite any theories or ideas! This has been baffling me for well over thirty years...