The Arms Room Concept

How multi-disciplinary Marines provide maximum flexibility to a distributed force

>Capt Sanderfield is currently serving as the Operations Officer for 1/2 Mar. He was the Company Commander for Alpha Company, the experimental Force Design 2030 company from July 2021 to April 2023.


The character of war is changing, and the Commandant has taken ambitious steps to redesign the force to confront a capable adversary in the Pacific. One of the most contentious aspects of the Commandant’s Force Design initiative is the Arms Room Concept. Under this concept, the Marine Corps infantry would transition away from some specifically defined MOSs to a force that leverages a multi-disciplinary Marine capable of employing a variety of different weapons systems on the battlefield. Responding to a question about the Arms Room Concept, BGen Watson, Commanding Gen Marine Corps Warfighting Lab said, “So the arms room means that you would have a sort of an armory of many different systems, and your Marines would be trained in all of them, and then you pick the weapons suited to the mission … as opposed to having single-threat Marines who are only experts at one system.”(1) As a company commander of Alpha Company 1/2 Mar, an experimental Force Design 2030 rifle company, my team and I have been on the forefront of creating multi-disciplinary Marines utilizing the Arms Room Concept over the last eighteen months. This period has resulted in many lessons learned and recommendations on how infantry battalions can overcome systematic shortfalls and effectively implement the Arms Room Concept going forward. With additional investments of time, resources, and an adjusted approach to enlisted infantry schooling, infantry battalions can employ multi-disciplinary Marines to provide maximum flexibility on a chaotic and distributed battlefield.

The push towards the development of the multi-disciplinary Marine is not one of desire, but one of necessity. Static positions and massed formations are terribly easy to find and target, especially against an adversary like Russia and China who possess a robust suite of sensors and persistent ISR capabilities. However, as this technology continues to develop and spread, it is no longer just the major power players who possess the ability to leverage space-based ISR platforms and unmanned-aerial systems to hunt their adversaries. These systems, coupled with precision-guided missiles, long-range rockets, and cheap loitering over-the-horizon suicide drones will force military formations to become smaller and more dispersed to survive. Operating within this type of environment makes it no longer tenable to train Marines to become experts at one singular weapons system. As formations operate further away from their higher headquarters, small units will be required to possess a multitude of assets, weaponry, and capability sets.

The common question that comes up when discussing the creation of multi-disciplinary Marines is which weapons systems should encompass the arms room and which capabilities will require a Marine with a specific MOS. While training every Marine to become proficient and qualified in every weapons system is desirable, it is unrealistic in application. Within Alpha Company’s Force Design structure, specialty-trained Marines and weapons traditionally held at the battalion level, such as Javelin missiles, heavy machineguns, mortars, and loitering munitions, have been transferred from what was previously weapons company to the company’s hunter killer platoon. These complex weapons systems require Marines with advanced-level training and were not included in our training to create multi-disciplinary Marines.

What Does the Arms Room Concept Provide the Service?
Flexible/adaptive force
A leading benefit of the Arms Room Concept has been the flexibility it has provided the company. As the 2nd MarDiv Experimental Force Design rifle company within 1/2 Mar, the company had the privilege of executing a series of difficult experimental training exercises across the United States. These exercises were designed to push the limits of an infantry company, employing advanced sensors and weaponry within exercise scenarios for the company to distances exceeding 50 kilometers from the rest of the battalion. In each of these instances, the company’s platoons and squads were distributed another five-ten kilometers to accomplish independent tasks assigned by the company commander. Upon insertion of the company into the exercise operational area frequently dominated by adversary sensors and anti-air missile systems, there was virtually no ability to adjust or reallocate key assets or crew-served weapons across formations. Doing so would require the use of already limited transportation platforms and would expose the force to the risk of detection and subsequent targeting.

Alpha Company’s employment of multi-disciplinary Marines and access to previously held battalion-level assets at the company level were key components that enabled success in a distributed operating environment. By having medium machineguns, rockets, long-range precision rifles, and recoilless rifles within each platoon, platoon commanders and squad leaders have the unique ability to custom tailor their table of equipment to provide a mission-ready force to accomplish the task assigned. For the platoons and squads within Alpha Company, this has at times resulted in one squad carrying multiple medium machineguns and rocket systems while another is operating with a much lighter footprint carrying only their primary service rifle into the fight. Only by training Marines on every weapons system could these custom-tailored units have the flexibility required to be successful in a distributed fight against a capable adversary while simultaneously possessing the firepower required to mass when necessary.

Redundancy is another beneficial aspect of the Arms Room Concept. If the Marine who is typically responsible for employing the medium machinegun or Carl Gustav recoilless rifle is incapacitated, there is a squad’s worth of Marines who can pick it up and employ it effectively in the fight. This occurred during several of our exercises and will undoubtedly happen in the next big conflict. While the most common example included a simulated casualty for the Marine carrying a specific weapons system, there were other instances where a Marine became ill or was simply needed to execute some other task. By having this redundancy, the unit never lost the capability that the weapons system provided because there was a ready bench of capable Marines who could pick up and employ that weapons system in the fight effectively.

Redundant capabilities have additional benefits beyond providing a company with a strong bench of utility players. It provides the option to weigh units in a way that was not previously possible. By having thirteen Marines who are trained to employ the medium machinegun or recoilless rifle within a squad, a company commander has the option to weigh that unit with additional weapons to allow for the accomplishment of a task such as an attack by fire or support by fire. The availability of these options has undoubtedly made the unit a more capable, flexible, and deadly force.

It is important to note that although redundancy means that a squad could theoretically hand a medium machinegun, grenade launcher, or recoilless rifle to any Marine within the squad to effectively employ, naturally the proficiency levels amongst the Marines will vary. We have addressed this by striving to train all Marines to be incidental operators with each of the weapons within the Arms Room. This means mandatory, across-the-board cross-training built into the training schedule to ensure every Marine can at least pick up a weapon, load it properly, conduct appropriate misfire procedures, and manipulate a machinegun’s traversing and elevation mechanism or a recoilless rifle’s sight system to engage various targets on the battlefield.

Enhances Integration
A point often used to argue against the Arms Room Concept is that there is no requirement to have these weapons capabilities organic to the rifle platoons and squads, for they can be attached by the company if required. While this argument is true on the surface, it overlooks the significant benefit of having Marines with those capabilities organic to each small unit. By platoons having access to the weapons and Marines during training, they will be best postured to accurately understand their capabilities, limitations, and how to best employ them on the battlefield. The valuable trust built through time and repetitions cannot be replicated with an attachment that may or may not have worked with the unit before. Instead of receiving an attachment whose true physical capability and overall proficiency are unknown and largely assumed, the Marines are already an organic part of that small unit. Under the new construct that employs multi-disciplinary Marines, a single rifle platoon can serve as a heavy support-by-fire element complete with a full complement of machineguns while also providing organic internal security. Previously, this same task would require several attachments from outside the platoon to accomplish. Now, each platoon commander and squad leader have the capabilities required within their units with their multi-disciplinary Marines.

The implementation of the Arms Room Concept provides the Marine Corps infantry with a much more capable, lethal, and flexible force, but it does come at a significant cost. To create highly proficient multi-disciplinary Marines, the Marine Corps will have to adjust the way we man, train, and equip future infantry formations. Below are some recommendations for how infantry company commanders can approach this issue to support its implementation and future use across every infantry battalion.

Building Capabilities Incrementally
Training all Marines within an infantry rifle squad to effectively employ every weapons system available does take an extraordinary amount of time and energy. That said, it is achievable if you take an incremental approach to building capabilities over time. Those who typically push back on the concept will point out that it is impossible for every Marine to have the same level of proficiency as a current machine gunner who has years of fleet experience and advanced-level training. However, the goal of the Arms Room Concept is not to blindly hand weapons to any Marine in your formation and expect the same results. Instead, the goal is to create highly lethal teams made up of multi-disciplinary Marines who can perform a laundry list of tasks and employ a variety of weapons systems. With a future operating environment characterized by contested airspace and severe distribution of maneuvering forces, Marine Corps units cannot afford to fill a critical seat on any insert helicopter with someone who can only carry out one singular task or employ one specific weapon.

Critics of the Arms Room Concept express concern about losing a level of technical proficiency by moving away from designated Marines who employ some of these weapons in the previous, legacy construct. Although a valid concern, the argument tends to exaggerate the complexity of certain weapons while also ignoring that the Marine Corps has long trained Marines to employ multiple weapons systems. Combat engineers and artillerymen each cross-train Marines to employ machineguns for localized security. Even within the infantry, squads for decades trained traditional riflemen to employ the M249 squad automatic weapon, a light machinegun organic within each fire team. Marines carrying this machinegun achieved much success in combat operations in Iraq and Afghanistan before the Corps transitioned to the current service rifle.

To accomplish our goal of incrementally creating multi-functional Marines who can employ each weapons system in the Arms Room Concept, Alpha Company started by selecting the most common weapons systems the squad would likely use on the battlefield. These included the Infantry Automatic Rifle, the M320 grenade launcher, Carl Gustav recoilless rifle, and the M240 medium machinegun. With the agreed-upon understanding that it would take a large amount of time and ammunition for all Marines to become experts on each of these weapons, we started by qualifying every Marine on the basics, such as the ability to load, unload, and conduct misfire procedures for each weapon. As each Marine effectively demonstrated the ability to conduct these incidental-operator-level tasks, they were classified as qualified Marines capable of employing this weapons system if required. As each Marine trained to become qualified, small-unit leaders identified top performers who were evaluated in employing that weapon on a live-fire range. Those who were successful in this evaluation were designated as certified on that weapon and could now fire that weapon system in support of a maneuvering friendly element. Over the course of the pre-deployment workup, the company was able to qualify nearly every Marine in the rifle platoons on each weapon system while also building an impressive number of certified Marines who were the first ones within that unit to employ the weapon if the requirement was identified during planning.

Use of Simulators to Build Proficiency
Certifying every Marine on each weapon within the Arms Room Concept would require a massive increase in the amount of ammunition typically available to each infantry battalion. To continue to train multi-disciplinary Marines under this resource constraint, infantry companies will need to maximize the use of technology and simulators. The Marine Corps has made great strides over the years to ensure Marines have access to realistic simulators to train and build proficiency, and these systems will only get better as technology improves and becomes cheaper to replicate. Currently, every base installation has an Indoor Simulated Marksmanship Trainer (ISMT) available for units to schedule and use for training. Although Alpha Company did leverage these systems to a limited degree, this is admittedly a resource we should have used more. Company commanders should embrace the use of available simulators and incorporate them into their weekly training schedules to build individual weapons capabilities without expending the limited ammunition available.

Although the ISMT is a valuable resource for training Marines, there are currently several limitations associated with these systems. First, the limited number of simulators available on each installation will be insufficient to support every infantry battalion as they each transition to the Arms Room Concept. Either the current ISMTs will need to expand, or additional facilities will need to be constructed to meet the increasing demand. There will also need to be an expansion of weapon systems available within the current ISMTs to ensure they encompass the M320 and Carl Gustav, critical weapons within the arms room. Another option could be the investment in an ISMT type similar within each infantry battalion’s office space. While this would require significant initial investment and continued attention to keep them working and operational, the benefits would be well worth the cost. 1/2 Mar has seen the benefit of having an in-house simulator first-hand. Within a battalion command post, there is a dedicated training room with multiple Javelin and TOW missile simulators. Utilizing these training aids does not require an extensive request process or deconflicting with dozens of other units across the base. As a result, the company and battalion have been able to sustain proficiency with these weapons systems while building an impressive number of incidental operators despite not receiving the necessary number of missiles to train effectively. With additional investment in the access and quality of simulators, infantry units can overcome the limited availability of live ammunition and develop a capable unit of multi-disciplinary Marines.

Leverage/Create Subject-Matter Experts
The Arms Room Concept and the creation of multi-disciplinary Marines within infantry battalions are only possible through the possession of unit internal instructors and subject-matter experts to train Marines on the technical proficiency necessary to employ various weapon systems. Alpha Company, 1/2 Mar has been fortunate in this area. To achieve the task organization in the company that included an increased rank requirement, the rifle squads were built from Marines from every infantry MOS. This was particularly important at the small-unit leader level. Each squad was comprised of staff sergeant squad leaders, sergeant team leaders, and several junior NCOs who were school-trained machine gunners, mortarmen, and anti-armor Marines. The presence of this diverse set of skill sets allowed the company to leverage these warriors to develop a team of multi-disciplinary Marines within each rifle platoon.

As infantry battalions adopt the Arms Room Concept and explore ways to replace the different specialty MOSs into a consolidated all-encompassing 03XX MOS, the Marine Corps must ensure units have access to a bullpen of school-trained instructors to fill this critical role. Until the Advanced School of Infantry redesigns its infantry school pipeline to meet this new challenge, infantry battalions must continue to leverage courses such as Advanced Machine Gunners Course, Advanced Anti-Tank Missile Gunner Course, and Infantry Unit Leaders Course. Marines returning from these courses will have the technical proficiency necessary to help develop and train the other Marines in their platoons. In addition to maximizing the use of these current advanced schools to train Marines and build a cadre of capable instructors, each infantry division needs to play a part by crafting division schools that help units achieve the goal of creating multi-disciplinary Marines across their formations.

Warfare is experiencing a technological revolution where precision-guided munitions and unmanned systems will continue to proliferate and dominate the future battlefield. To meet the challenge of a future fight against a smart and capable near-peer or peer adversary, the Marine Corps infantry will need to transition away from a force of single-threat Marines to a more capable and flexible team of multi-disciplinary Marines capable of employing a variety of different weapons available within the unit’s armory. While Alpha Company 1/2 Mar has made a tremendous number of mistakes along the way and certainly does not have all the answers, our experience on the cutting edge of Force Design 2030 experimentation for the past eighteen months has informed us of the benefits of Arms Room Concept and the necessity of multi-disciplinary Marines within the infantry. With additional investments of time, resources, and an adjusted approach to enlisted infantry schooling, infantry battalions can employ multi-disciplinary Marines to provide maximum flexibility on a chaotic and distributed battlefield.


1. Megan Eckstein, “Marines Update Force Design 2030 After a Year of Experimentation in the Field,” United States Naval Institute News, April 26, 2021,