The 4.2 inch M2 mortar was a rifled
muzzle-loading weapon designed for high-angle
fire.
Weight, 4.2 in M2 mortar, complete: 333 lb.
Barrel, M2: 105 lb
Base plate, M2A1: 175 lb
Standard, M1: 53 lb
Dimensions:
Barrel: 48 in long, inside diam 4.2-in between
lands
Rifling: 42 in long, makes one half turn,
Base Plate: Rectangular, 26x28 in
Tube cap and striker pin cast in one piece,
screwed on the tube
Standard: Support base with elevating and
recoil mechanism.
Support base plate: 6x24.5 in
Rate of fire:
First 2 minutes: 40 rounds
First 20 minutes: 100 rounds
Prolonged fire: 60 rounds per hour
Range:
Maximum: 4,400 yds
Minimum: 565 yds
Ammunition:
High Explosive: M3(w/M9 Fuze): 4.19 in ID; 20.4
in long; 24.5 lbs
High Explosive: M3(w/M5 Fuze): 22.0 in long;
25.5 lbs
Smoke, WP, M2: 20.4 in long, 25.5 lbs
Smoke, FS, M2: 20.4 in long; 25.5 lb
Gas, Irritant, CNS M2: 20.4 in long; 25.0
lb
Ammunition:
Ammunition for the 4.2-inch
mortar was of the semifixed complete type. All
parts of the round were loaded in the mortar as
a unit and in one operation, but the propelling
charge was varied for different ranges. A
complete round consisted of a fixed shell,
fuze, and a propelling charge. The propelling
charge consisted of an ignition cartridge and a
number of powder charges. The ignition
cartridge was inserted into a cartridge
container that was screwed to the base of the
shell. The powder charges were placed on the
outside of the cartridge container and held in
place by an adjustable propellant holder and a
striker nut.
When fired, the shell was
stabilized in flight by rotation transmitted to
the shell by means of the pressure plate
expanding the rotating disk on the base of the
shell thus forcing the disk to engage the
rifling in the bore. The shell, which had a
deep cavity and suplementary charge, was fitted
with a point detonating fuze. The ignition
cartridge was housed in the cartridge container
extension and was held in place by the striker
nut which contained the striker. The propelling
charge consisted of a number of increments of
propellent powder in the form of square sheets
assembled on the cartridge container. When the
round was inserted into the bore and released,
it slid to the bottom where the firing pin
drove the striker into the primer of the
ignition cartridge. Flame from the ignition
cartridge flashed through vents in the
cartridge container extension to ignite the
propellant, thus firing the round.
Because of its size and weight,
the weapon was used as Regimental artillery,
often vehicle mounted. A 4.2 mortar squad had 8
men, with 4 squads in a 4.2 in. mortar platoon.
In the Marine Corps, each Rifle Battalion had a
Weapons Company, with 60 and 81 mm mortars, and
heavy machine guns. Each Rifle Regiment had a
4.2 inch mortar company with 12 guns,
supporting the Rifle Battalions as needed.
These heavy mortars were almost as effective as
the Chinese 120
mm, the heaviest artillery available to the
infantry divisions when they assaulted Eighth Army and X Corps at
Chosin.
Song Shilun's 9th Army
Group, consisting of 4 armies, of 12 divisions
and about 120,000 men, threw almost all its
strength at the three Infantry Regiments of the
US First Marine Division. The successful
withdrawal by the Marines, while destroying the
CCF divisions as effective fighting units for
the balance of the Korean War, was greatly
assisted by the fortunate proximity of
Divisional light and medium artillery, and
constant and devastating air to ground support.
But that was not the main reason 1st Marine
Divison survived. Eighth Army on the West Coast
had even more artillery and air support, and
much more armor, and yet they were completely
routed by a CCF force approximately of the size
that was fought off by the single division of
Marines.
The basic reason the Marines
performed so brilliantly was that they were
psychologically prepared to fight, and to die
if necessary, and were thoroughly trained and
experienced in effectively deploying all the
basic weapons of an Infantry Division. In that
regard, the 60 mm mortars deployed with each
platoon, supported by the 81 mm mortars at
Battalion, and even more powerfully by the 4.2
in mortars at Regiment, were well targeted, and
savagely effective.
It was the men who closed with
the CCF at the unit level, fought them to a
standstill, identified appropriate targets and
exploited the use of mortars and machine guns
that were deployed against those targets, who
made the difference.
In war, it will always be the
men who make the most vital difference. But, it
sure helps for them to have plenty of effective
weapons at hand!