I don't know if it is use any more and I don't know if it would mount up to the RV buss on MMIII. Communications have advanced so much since the late 60s it probably isn't in use.
Emergency Rocket Communication System is what is was. The Air Force (we) used to go out and swap these packages around regularly to keep the Soviets guessing as to where they were. They watched us, we watched them.
Some days we were dispatched to a site with no work orders. It could have been an ERCS site or a site with a regular BT. We would open the PAH and lower tools and a couple of drawer cases and our TO box full of binders.
After the penetration checklist was ran, we would check seals, check for indicator lamps that were out, do a little light housekeeping, and then settle in for a few hours of spades, or hearts, have lunch, or just shoot the Scheiße. After a few hours, we'd call JC and start the backout and go to the next site and do it again. Other ERCS and non-ERCS sites we really did have maintenance to perform, but was not usually ERCS related. We just didn't want the Soviets to know where these comm packs were located.
They would also send MMT (Missile Maintenance Team) out with an RV van and park it over the door and roll the door back, and pretty much have the same kind of day we had. Their tasks to get that door open was a lot more involved than what we had to do to get in. They would only do one site a day, while we might do three.
During annual code change, that was the dispatch you wanted to be on. All we did was load missile targeting data all day. Usually, but not always, the site was already open by an MMT team, so all we had to do was authenticate onto the site and go to work. If we were there more than an hour something was wrong. We could do about six or eight sites in a day depending upon where the sites were and how easy it was to drive between sites. No site was closer than three miles from the next, but they were usually a lot farther than that. Those were the only dispatches where the entire team was armed. and we took an extra guard with an M-60 or M-249.
If we had to penetrate the sites ourselves, we might only do four sites on a dispatch, or even only three.