Infantry Unit Tactics, Tasks, Weapons, and Organization

[Fuchs]

Staying in that nation, FM 6-30 clearly shows that massing fires is about one battalion of arty or more, in 1-3. A single Bty is shown as non-massed fire example.

(16 July 91 version of FM 6-30)

A battery is the basic firing unit. Splitting up batteries in demibatteries was known for centuries, but a battery is still the basic unit. A basic unit's fire is hardly "massing fires".