(Wikie talks about American Airlines being the largest operator but it was Allegheney before they were bought out by AA I think?)
I believe the original American operator of the BAC was Mohawk Airlines, based in Ithica, NY. Mohawk was absorbed into Allegheny which later became USAir. Allegheny had a flock of them. I can't remember the Mk of the original Mohawk BAC's, but I seem to remember they had an altitude restriction because they weren't equipped with drop down O2 masks. Braniff also ran the BAC1-11 I believe. If anybody at BAC had had the foresight later shown by Dee Howard and equipped the aircraft with RR Tays, it would have been a whole other ball game in my opinion.
Edited to add a link to some piccies.
George Hamlin Mohawk photos.