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M2 4.2 inch Mortar and Manuals

The M2, although with assembled weight of 333 lbs, was considered a portable Regimental artillery support weapon. Its sturdy rifled M2 barrel and gave it a maximum range of 4400 yards. Concentrated HE and White Phosphorous Smoke shells were deployed in the majority of its missions, and the weapon gave vital support to the 1st Marine Division in its savage fight-out from the encircling Chinese Divisions at the Chosin Reservoir in the Korean War. The M30 Chemical Mortar provided the same diversity of mortar shells but, although at double the weight, had a much more useful range of 6500 yards and gradually displaced the M2.


FM 23-91:Mortar Gunnery

FM 23-91:Training Strategy


4.2 inch M30 Mortar

A 4.2 inch M2 mortar crew, members of reconstituted Task Force Smith's 21st Infantry Regiment, fires on attacking North Korean 4th Division assault troops near Chochiwan, 11 July 1950. With their 3rd Battalion routed in front, and enemy blockades in their rear, well overmatched against the veteran NK 4th division with their supporting tanks, our positions here were soon again over-run and our surviving troops again had to escape however they might, if they might.



4.2 inch M30 Mortar

4.2 inch M2 Mortar

4.2in M30           60mm Mortar           81mm Mortar

Commonwealth Division 3in mortar in night action

2d Chemical Mortar Battalion


4.2 inch M2 Mortar
A 4.2-inch M30 mortar crew of the Heavy Mortar Company, 179th Regiment, 45th U.S. Infantry Division, fires on Communist positions, west of Chorwon, Korea, 5 May 1952.

The 4.2 inch M2 mortar was a portable weapon! The M30 exchanged this feature for increased range.


General Data

  • 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!


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