[Yossarian]

A 737 cargo carrier has only two people on board?

Let's see:

1. Pilot
2. Co-pilot
3. shouldn't there be some kind of loadmaster?

[HeadOn]

No loadmaster needed. Cargo safely anchored in closed “cans” or on pallets before takeoff. Mechanical locks on the cargo deck. Fire suppression system activated from cockpit if needed.