The TT-333 transmitter group is used in torn tape relay sites to feed 3 or 6 outgoing lines. 

Each TD has an associated message numbering unit which automatically inserts a channel ID and message number before each transmitted tape. 

In 3- channel configuration, two TD units feed the same channel in ping/pong fashion. So you can load a new tape into the lower one of a pair while the upper one is transmitting and then at the end of the first one, the second will automatically start, and so forth. There are relays that control all the sequential operations. 

I have created one of these units although I didn’t have a cabinet. You can see a video of it in operation at

The torn tape relay system description is here

I wish that surplus unit was located closer!