From what I recall, back c1970 three innovations in water delivery were adopted.
1) Rapid Water aka Slippery Water, a wetting agent that enhanced the flow prob by reducing surface tension thus friction loss. It was introduced into the pump via a proportioner similar to foam concentrate. The trade name "slippery" was appropriate, as it was reported members were slipping and sliding and being injured after losing their footing on the wet surfaces.
2) I'm no expert on hydraulics, but a new type of "constant flow" nozzle was tried, which was supposed to increase the gpm delivery at the nob. This was different from the "NPO" or "No Pump Operator" gadget whereas adjustments at the nozzle, relayed instructions [maybe via RF] to the pump panel. I think E257 and maybe E298 used this experimental rig for a spell.
3) Converting from 1 1/2" to 1 3/4" hose for increased gpm.
Any one of these methods would have possibly given the desired effect. Trying all three at once was probably overkill.
I won't swear to any of this, but it is how I remember it. Other comments welcome.