What is "plunging fire"

Plunge \Plunge\, v. i.

1. To thrust or cast one's self into water or other fluid; to submerge one's self; to dive, or to rush in; as, he plunged into the river. Also used figuratively; as, to plunge into debt.

   Forced to plunge naked in the raging sea.
   --Dryden.

   To plunge into guilt of a murther.
   --Tillotson.

2. To pitch or throw one's self headlong or violently forward, as a horse does.

   Some wild colt, which . . . flings and plunges.
   --Bp. Hall.

3. To bet heavily and with seeming recklessness on a race, or other contest; in an extended sense, to risk large sums in hazardous speculations. [Cant]

   Plunging fire (Gun.), firing directed upon an enemy from an elevated position.

Plunging fire is a form of indirect fire, gunfire fired at a trajectory such as to fall on its target from above. It is normal at the high trajectories used to attain long range, and can be used deliberately to attack a target not susceptible to direct or grazing fire due to not being in direct line of sight.

In naval warfare plunging shellfire was often used to penetrate an enemy ship's thinner deck armor rather than firing directly at a warship's heavily- armored side.

Plunging fire in terrestrial warfare allows attacking a target not in direct line of sight, for example over the brow of a hill. Artillery weapons such as howitzers and mortars are designed for this purpose. Machine guns and belt-fed grenade launchers may also use plunging fire.