air brake control on 5 ton

I have a M139 5 ton truck This was originally a bridge tender truck so it has the 14.00x 20 tires and double frame. I have taken the box off and hopefully will make it into a tractor/trailer unit.
My question has to do with the air brake control lever on the steering wheel shaft. Is that lever supposed to control trailer brakes? My cousin who was in the Army back in the 70's in Germany remembers that all the trucks had trailers, but didn't pay enough attention to whether the trailers used air brakes( he was a radio operator, not a truck driver)
So repeating myself, Does that lever on the steering column control trailer brakes?

Yes.

Also, please include a state in your location as the site rules request.

Yes, That used to be called a 'Hill Holder' on the Scammell tank transporters.
Also Used as a trailer brake.
Note (That) The FRONT glad hands (are not 'operated' by the Hand Control Valve (and)) do not exude air with the operation of the Hand Control Valve.
The front glad-hands are Input air to brake the vehicle when towed. And to fill the air supply on the truck being towed.

It is also called a Johnny Bar/Brake/Arm.

Main use is to lock trailer brakes while backing the tractor under it to hook up, or forward to disengage, so the trailer doesn't roll during those operations. You hook up your air lines first, of course.

I use it to check that the 5th wheel is locked properly each time I start to move. (If you've ever had some dillweed pull your 5th wheel release while you are parked, you become meticulous about that check. Fortunately for me I learned that lesson vicariously watching someone else drive out from under his trailer at a truck stop).

It can be used to check your brake lights (lock the trailer brakes, go back and have a look).

Cheers