Originally Posted by FlyJSH

Clearance delivery circa 1959:

During this pause in the operation he begins to issue the ATC clearances. It went something like this: Ground Control -"The following flights listen for your IFR clearances and read them back in the order given. ATC clears United 723 to the DEN airport...........ATC clears TWA 452 to the Kansas City airport.........ATC clears American 124 to the Tulsa airport.........ATC clears North Central 17 to the MKE airport........ATC clears Capital 654 to the CLE airport...... Go ahead United 723 with your read back!" They usually issued the clearances in batches of 5 or 6 at a crack and heaven help the F/O (first officer) who "muffed" his read back! And so the process went. After a batch of clearances were read and acknowledged, then another group of aircraft would be issued taxi instructions followed by ATC clearances.