I was part of the retrograde in 2011/2012, the first time an administration thought leaving was a good idea. I didn't do the actual retrograde work, my unit was designated to continue operations, but I did have to inspect gear they proposed sending back.
- Gear has to be extremely clean in order to send it back. It has to have every bit of sand removed from it, and I mean every. This order comes from customs.
- Once the above requirement is at-play there becomes a cost benefit analysis to what gear is worth taking and what's not. The remaining gear is usually destroyed somehow and possibly buried. This includes gun parts and attachments.
- the effort to snag gear from small bases like observation posts is difficult. Some of these places are in military advantageous places, which also make them difficult places to get vehicles to. If you can't get a logtrain there, then you've got to fly a helicopter. The Taliban are no stranger to setting off the rocket detection systems on helicopters.
- retrograde is literally spare troops sitting around hand scrubbing gear on a very long and boring deployment. I felt terrible for these people. Morale is always low in these units.
The last way I can think of is the most infuriating. I don't know how to speak to this scenario without telling a story, so here goes:
I was in a region called Musa Qalah. My truck was ordered to help bolster operational capabilities while a base was handed over to the Afghan National Army. The base was called Habib. On our way there we encountered a truck loaded down openly with munitions and jovial men that was weaving in and out of our convoy. When we requested permission to engage with what was obviously a hostile truck we were reminded that the Rules of Engagement as set by the administration were, "You're not to fire until you have been fired upon." The truck eventually detoured from us and we arrived at the base. It was a small place, maybe 8-10 posts in total. Marines had been using it to patrol the nearby town and keep the area peaceful (generally the Taliban will attack the base instead of infesting the town, which is a bit of a pseudo-win while schools and infrastructure get in queue to be opened up). It was a pretty average base from what I saw. Lots of concertina wire, the posts were sandbagged but not the most built up. Decent fighting positions though. The units doing stage one of the retrograde (collect all the gear) were doing their thing. I did see the ANA at some point. We tend to leave them with gear like minesweepers, radios, (I could see bioscanners being part of this). Basically anything the average infantry unit would need. The thing I noted is that there were only 8 ANA including the commander. On the last day I was watching the mountains outside of the base and I saw a series of figures on top of the mountains. Initially dismissed as goat herders, I started watching them through my rifle scope. They were holding guns and there were munitions crates stacked all along the horizon. They were waiting. No more ANA showed up. 8 people to staff 10 posts. We were told the mission was to turn over the base to the ANA and that staying behind to help them defend would be counter to that mission. We left. Habib went dark on radio over the next two days.
It's possible the ANA took their gear and left, they made a deal with the Taliban, or that they were slaughtered. You can imagine where the gear goes when troops aren't prepared for how to destroy it properly or don't have the tools necessary.