More Mortars for Marines

The Regimental Mortar Company of 1949

Dec 15, 2025

The K-Series tables of organization for infantry battalions might well have been stamped with the motto ‘back to the future’. A slogan of that sort, however, would not have applied to the direct descendants of the regimental weapons companies of the Second World War. Thus, rather than providing each Marine infantry regiment with a unit armed with towed anti-tank guns and field pieces mounted in half-tracks, the authors of these establishments gave the ideal infantry regiment both an anti-tank company and a company of 4.2-inch heavy mortars.

In an article published in the Marine Corps Gazette in September of 1949, Henry Aplington, II, who had commanded the 1st Battalion, 3rd Marines on Guam in 1944, described the virtues of the definitive weapon of the new heavy mortar company.

A mortar, and less than one quarter the weight of the 75^mm pack howitzer, it can be hand carried ashore with the infantry. Its minimum range is about 700 yards (640 meters) making it very acceptable as artillery in shallow beachheads while its maximum range of 4,400 yards (4,000 meters) fits it to handle any mission considered too close for flat trajectory naval gunfire or the frequently erratic air strike. It can reach into defiladed approaches and its projectile carries a greater weight of high explosives than even the 105mm (howitzer shell). 

The 4.2 is a truly versatile weapon. Rifled, it packs artillery accuracy and fire power with the mobility of the 81^mm mortar. It can take advantage of small depressions or low walls to reduce its vulnerability.  At times in the last war, it was even fired from landing craft. It breaks down for carrying into three component parts, each of which can be packed by hand or carried on a hand cart.  It takes terrain that will stop a man to stop it.

I watched a battalion of them (the 82nd Chemical Battalion) come ashore on Arundel Island in the New Georgia group and start off through the jungle for the northern end of the island, from which, a few days later, they were firing on Japanese positions on (the nearby island of) Kolombangara, supplementing the fire of Marine 155^mm guns emplaced at Piru plantation.

The heaviest part of the 4.2 is the base plate which weighs 150 pounds; the short rifled barrel weighs 91 pounds, and the monopod or standard weighs 53. This weapon is heavy in comparison with the 136 pounds of the 81^mm mortar but extremely light and transportable in terms of our present divisional artillery or self-propelled full tracks. The assembled weapon weighing 294 pounds can be emplaced in five minutes by day and ten by night.

To bolster his case, Lieutenant Colonel Aplington quoted an officer of the US Army Chemical Corps, who, in a piece published in Military Review, compared the 4.2-inch mortar to the M-3 105^mm howitzer used by US Army cannon companies during World War II.

What brought about the adoption of the 4.2 in the infantry regiment? It is felt that this resulted from the fact that the infantry had found that they needed a heavy weapon in the cannon company of greater all around usefulness than the М-3 howitzer. From the standpoint of versatility, the heavy mortar fitted in best. In addition, the infantry had learned the tremendous effectiveness of screening smoke when properly laid down by a unit equipped with the right weapon and an efficient and effective shell. 

Another consideration, it is felt, was the desire of the infantry to have a weapon in the cannon company which could go with them wherever they might be called. Wherever human feet and hands can walk and climb with carried loads, there the 4.2 mortar can likewise be found.

In keeping with this meeting of minds, the heavy mortar companies of Marine infantry regiments authorized in 1949 looked a lot like the heavy mortar companies given to US Army infantry regiments in 1948. In both outfits, a four-piece platoon, served as the basic building block. However, where the Army heavy mortar company fielded three forty-man mortar platoons, the Marine heavy mortar company made do with two forty-one man units of that type.

Heavy mortar companies of Army (left) and Marine Corps (right) infantry regiments

A platoon of either type broke down into four eight-man squads and a small headquarters. The Marine mortar platoon, however, received one more communicator than its US Army counterpart.