A few railroads converted cabooses to be remote control units to be MU'd to locomotives for RCO. This way they could use any locomotive as a Remote unit. I believe Norfolk southern and maybe CSX had flat cars with an electrical cabinet in the center that carried the remote control electronics. They were equipped with lights horn and bell per the rules too. very odd to see when it was out working.
The WC used these to experiment with one-man crews on the White Pine Branch in the '90s. As seen in this picture, they were used on the dumper jobs in Escanaba until the dock shut down a few years ago.