Complex sentence: It was the successor to the Postal Transportation Service (PTS); the PTS had responsibility for mail transportation contracting as well as employees assigned to Mobile Unit and stationary PTS facilities such as Air Mail Facility, Terminal Railway Post Office, or Transfer Office operations.
Split into simpler sentences: It was the successor to the Postal Transportation Service (PTS). The PTS had responsibility for mail transportation contracting as well as employees assigned to Mobile Unit and stationary PTS facilities such as Air Mail Facility, Terminal Railway Post Office, or Transfer Office operations.