All 3 Uses

impervious
in
Flags of Our Fathers
(Auto-generated)

The Japanese had installed more than 750 blockhouses and pillboxes around the island: little igloos of rounded concrete, reinforced with steel rods to make them virtually impervious even to artillery rounds.†
Chpt 1.
It was the mission of boot camp to quickly convert recruits' naive boyish fervor into something American society had never generated before: a mass-produced, numerically immense cadre of warrior-specialists at once technically sophisticated and emotionally impervious to the horrors of battle.†
Chpt 3.
The Japanese were building defenses impervious to our bombs.†
Chpt 4. *

Definitions:

(1) (impervious)
not admitting passage through; or not capable of being affected
(2) (meaning too rare to warrant focus)