There is one part of the munitions that still remains a mystery. It's acquired the nickname of the "bicycle pump", and has been shown in relation to three of the munitions recorded by groups in Syria. The most complete example has been shown in a video that shows an unexploded example of the high explosive variant of the UMLACA being dismantled
The "bicycle pump" can be see at the start of the video, and later on the ground next to the munition
What appears to be the partial remains of the "bicycle pump" also appears in two other videos, from munitions linked to alleged chemical attacks
It appears these are possibly two different sections, with a screw thread visible on the piece with possibly wires or cables sticking out the other end. I put together the following image to compare the different objects
The other question is where does it actually go? Some people have suggested it could be a fuze, but I don't think that's possible, at least in the version of the UMLACA linked to the chemical attack. The suggestion has been that it would sit in the middle of the central column of the warhead, shown below
The problem with that theory is what's at the front end of that central column
This large metal plug would make it impossible for anything to extend into the central column. My current theory is this metal plug would have sat part way down the central column, with the explosive charge sat on top of that. This would force energy of the explosion sideways, bursting open the outer skin of the warhead. This would account for the bending and sheering of the metal we can see in the above picture.
So, that seems to eliminate the front of the warhead as the location of the "bicycle pump". On the other end of the warhead we have another candidate:
These two ports either side of the central column are present in the UMLACA linked to chemical attacks, while the high explosive type only appears to have one port. The port on the left side appears as if it can be some sort of access port, and is generally shown to be even sealed, as shown above, or heavily damaged and broken. The port on the right side appears to be open in all the videos, and in the videos showing the HE version of the UMLACA, which only have one port, its also appears to be always open, as shown below
This might point towards a common type of port on both type. The below images show the view of the ports from inside the munition, with the open port at the top
While considering these ports, it might also be relevant to consider the following video, showing the launch of the same type of munition
At around 4m 20s it appears the man wearing red is screwing something in or out of the base of the warhead. At 6m 20s he appears to be attaching a cable to the same position, and then gets off the truck, and seems to indicate to everyone else to leave. Minutes later the rocket is launched. Could this be the rocket being prepared for launch, and if it is, does it relate to the hole in the rear of the warhead?
So far, no-one has been able to identify the "bicycle pump", but it seems it's a key part of understanding how this munition works, and may give some clues to it's origins.
More posted on the subject of the August 21st attacks can be found here, and other posts on chemical weapons and Syria, including extremely informative interviews with chemical weapon specialists, can be found here.
You can contact the author on Twitter @brown_moses or by email at firstname.lastname@example.org.