Competition
BAC BAC 1-11
The primary threat to the DC-9-10 and launched prior to the DC-9.
Boeing B737
The main competition for Douglas, but got out of the gate late. It would take the Boeing B737 20 years to catch the DC-9.
SUD SE.210 Caravelle
First to be launched, but was never really a threat in the US. United was the primary customer for this model.