The RAAF borrowed this system and trialed it in the 80,s using H models.
Modular Airborne FireFighting System - Wikipedia, the free encyclopedia
Don't know why it never went any further. They where operating out of Victoria from memory and would return to Richmond once a week to get serviced (clean all the fire retardend gunk out of the tailplane, yuk).
Here is a link to a report on the trial
Fire Research Reports - Report No. 15