The first quick release fittings were used on an integrated torso harness starting in World War 2, the Navy being the first to employ them on their aircraft because of the danger of crews walking across the carrier deck and getting blown overboard if the back parachute accidentally deployed. By having the pilot wear a integrated torso harness and having him hook into the ejection seat at the aircraft, this also saved him from lugging the heavy 'chute around. The Air Force began using a torso harness later in the early 1960s in the F-4 Phantom Aircraft. Jets that were designed earlier utilized a back-style parachute/torso harness, like the F-100 and F-105. In this article, we will show you the different styles of Ejection Seat / Torso Harness quick Release fittings from both the Navy and Air Force. At the right, you will see the 4 main quick release fittings broken down by service (Air Force / Navy) and by use (Seat Side / Harness). It is obvious from this picture how the Air Force and Navy seem to think they have to be totally different, basically exact opposites. 
The Navy's integrated torso harness is designated the MA-2 (or PCU-33). The MA-2 has a series of webbing straps going between the legs, over the shoulders, and across the chest. The pilot would put it on by slipping his legs through the leg loops and pulling it over his shoulders. There is a zipper in the front that closes the body material and then a chest strap is cinched. The early MA-2s had the body material coving the entire strap system. Most pilots found this full-body material restrictive and uncomfortable.  Some studies were done and it was found that the full-body material provide no extra support and was basically unnecessary, so the ALSE Techs were able to cut the lower body material away from around 1966 through the early 1980s.  Around 1983, the MA-2s were being manufactured without the lower body material. This type of MA-2 is still being used today.  The MA-2 torso harness used 2 sets of quick release fittings. 2 at the shoulder (upper) for attaching the parachute riser and 2 at the waist/crotch area (lower) for attaching the survival seat kit so upon ejection, it would stay with the crewmember. Another difference in the early and later MA-2s is the style of life/extraction ring used. The extraction ring was used in case the crewmember had ejected, it gave a rescue helicopter a solid point to attach a winch to and pull him to safety. The MA-2s were issued with a small V life ring from the late 1950s through the late 1970s. In the early 1970s, after use in Vietnam showed the small V ring was sometimes difficult to hook to if injured or under fire, the crewmembers began putting large carabineers on their MA-2 harness too. In 1974, the military got the picture and began have the MA-2s made with large snap life rings in place of the small V ring.
The first type of harness quick release fittings were made by the Rocket Jet Engineering Company (RJE) in the 1950s. This type of quick release fitting was used on aircraft like the F-8 Crusader to the OV-1 Bronco. The RJE fitting was used primarily by the US Navy and Marine Corps, with the exception of limited use by the Army in the OV-1 Bronco aircraft. From introduction the 1950s through mid-1960s the RJE fitting was used on the upper and lower points of the MA-2. In the 1960s another company came up with a superior designed quick release fitting, H. Koch and Sons introduced what is simply called the Koch fitting.  The large male Koch fitting began seeing squadron use in the mid-1960s and was used early on with the lower RJE fitting. Eventually, Koch and Sons made a miniature male Koch fitting to replace* the lower RJE fitting. These were seen in the squadrons around 1968, but not in quantities until around 1970. The upper Kochs on the MA-2 are called "Large Male Kochs" while the lower Kochs are called "Mini Male Kochs." [As a side note, the US Army used the RJE fitting in the OV-1 aircraft well into the late 1970s- after that, they used the Navy Koch fittings on a specially designed harness that is basically a cross between the MA-2 and the Air Force PCU-15.]  Currently and since the 1970s, the US Navy and Marine Corps use the MA-2 with large male upper and mini male lower Kochs in all ejection seat aircraft.  Test pilots and High Altitude crews required a different type of torso harness, one that was not as restrictive with the body material. The harness was designated MA-2/P. Basically the same as the MA-2 with the exception of no body material and a ejector snap closure at the chest. These would use the same quick release fittings as stated above at those years. 

Air Force PCU-15 Harness

The US Air Force felt they had different requirements for their torso harness, so the similarities are minimal between the 2. The Air Force, as mentioned before, was a little slower in utilizing the integrated torso harness- first being used in the F-4 Phantom in the 1960s. The Air Force's first ejection seat integrated torso harness was designated PCU-3 and was designed for use on the Martin Baker MK-H5 ejection seat. Later variants were designated PCU-15 and PCU-15A/P. The PCU-3 (shown at left) was similar to the 15 & 15A/P with the exception of closure buckles- this will be discussed later. The basic PCU ejection harness has straps going between the legs, over the shoulder, and across the chest- sounds like the MA-2, doesn't it? That is where the similarities end though. The Air Force has their harness equipped with 3 closure buckles and rings. Each crotch strap and the chest strap can be unhooked. This allows the crewmember to be comfortable and unrestricted until getting into the aircraft where he will hook the crotch straps and chest strap. The PCU-3 harness used attachment buckles made by Koch, there is no similarity between the current Kochs fittings and the ones used on the PCU-3. The rare fittings on the PCU-3 are similar, except the chest strap clip has a removable pin and the 2 leg clips are threaded with the strap. The PCU-3 was used from 1963 until the late 1970s when it was replaced* by the PCU-15 and a new improved snap/buckle system (actually, a lot of the PCU-3 harnesses had their fittings replaced with the new and improved ejector snaps). The snaps on the later torso harnesses are called ejector snaps. This is because not only do they securely lock, but they also open and actually push the "V" ring out, thereby releasing the strap. One can only imagine how great this must be after getting shot down over enemy territory and trying to get out of the harness quickly. The V ring is the mate to the ejector snap, called such because it comes to a point where the snap meets it. The back of the harness has body material, but other than that, it is all heavy webbing straps. The underside of the shoulder straps has some thin padding for comfort. The PCU-15 ejection harness uses female upper Kochs for attaching the parachute risers and there are D rings at the hip area for hooking into the ejection seat survival kit. The PCU-15 harness is used with aircraft like the F-4 Phantom, F-15 Eagle. The PCU-15A/P ejection harness (shown at right with LPU-9/P Life Preserver attached)  uses Frost fittings at the shoulders for attaching to the parachute risers and D rings for the survival kit. The Frost fittings are uses only in the F-16 Fighting Falcon with the Aces II ejection seat. Though called Frost fittings (originally made by Frost Engineering), H Koch and Sons also make these fittings for the Air Force. 

* The word "replace" is used loosely. When a new item is introduced into the military supply system, it typically takes quite a while for it to get to every squadron and totally replace the other piece.