Mortars, Rockets, and Naval Gunfire

Mortars

Technically, any weapon designed only for high-angle fire is a mortar, but the most common use was the highly-portable short-barreled infantry support weapon.

In general, mortar fire will have the same effect as high-angle artillery from a shell of a similar size, or somewhat smaller. Another advantage is high rate-of-fire: Wesely gives a maximum rate of 27 rounds per minute (10 sustained) for an 81mm mortar; 18 and 3 for a 4.2" mortar. HC smoke was not available for US mortars -- only WP could be used. [2]

Rockets

Rocket artillery has these characteristics:

Distinctive flash and blast -- it's hard to miss where they came from and arrange counterbattery.
High volume and rate of fire -- a 4.5" battery with twelve rocket launchers can deliver 288 rockets in a twelve-second volley, and can sustain a rate of three volleys every four minutes. A 4.5" rocket has comparable effect to a 105mm HE shell. Sixteen 4.5" rockets will neutralize an area about 100×100 yards.
Less accuracy -- dispersion is high, so it's really only useful for area targets. They are not capable of direct fire. It is not suitable for use near friendly troops. Correction is still done, but it is on a salvo-by-salvo basis. Correction is done from previous points of fire (possibly with as few as 8 rockets) or from a firing bracket of 100-yard spaced shots. Map data is not normally used.
Shorter maximum range
Some flexibility -- quick, delay, and VT fuzes are available for HE and smoke projectiles. Open sheafs can easily be arranged along or perpendicular to line-of-fire.

Range dispersion decreases with range; lateral dispersion increases. The following table shows the area (yards) into which 68% of M16 rockets for a launcher are likely to fall:

Range (yards)	Range Dispersion × Lateral Dispersion (yards)
1000	900×105
2000	815×210
3000	720×310
4000	580×420
5000	380×520

Units may fire in converged sheaf, or open sheaf in either range (end-to-end) or lateral (side-by-side) configuration.

Naval Gunfire

Naval Gunfire had these advantages:

Gun variety and size, ammo choices
High rate-of-fire
High muzzle velocity (great against hard targets)
Small deflection pattern due to tight grouping of the guns
Good fire control equipment
Highly mobile
More flexible charges allow support on reverse slopes.

But it also has limitations:

Flat trajectories -- no high-angle fire (Weapons 6" and above are all guns, not howitzers. Smaller caliber guns were capable of high-elevation fire like howitzers).
Communication difficulties
Only correction from previous fire points are possible.
The ship may not be able to get to where it needs to be.
More range dispersion -- 2x to 3x ground artillery, with a deflection dispersion of only 10% of the range dispersion.
Limited ammunition
Enemy action may cause the cessation of supporting fire.

Misc. notes on Naval Gunfire in support of ground action:

Observation is done by Naval Liaison officers.
5" and bigger have the equivalent of HE; 6" and larger have AP; 3", 5", and 6" have illum; 3" and 5" have WP.
Most fuzes are available. VT is available for 3", 5" and 6", with a minimum range of 6,000 yards.

Observation

National Doctrine