This report provides a comprehensive analysis of the evolution of the purpose-built combat shotgun within the United States military and law enforcement, from its conceptual origins to its present-day role as a specialized tactical tool. The shotgun’s developmental trajectory has been cyclical, its relevance waxing and waning in response to the changing character of conflict. Its utility peaked in the close-quarters, high-lethality environments of World War I trench warfare, the jungles of the Pacific and Vietnam, and modern urban combat operations.

Key inflection points have defined this evolution. The first was the invention of a reliable, mass-producible repeating mechanism—the pump-action—perfected by John Moses Browning in the Winchester Model 1897. This transformed the shotgun from a simple fowling piece into a viable military weapon. A second, persistent theme has been the critical role of ammunition technology. The platform’s effectiveness was repeatedly hampered by the failure of commercial paper-hulled shotshells in harsh military environments, a problem only definitively solved with the advent of robust brass and, later, plastic-hulled cartridges.

The procurement philosophy has also shifted dramatically. Early “trench guns” were bespoke military variants of commercial designs. The Vietnam era saw the widespread adoption of inexpensive, off-the-shelf “riot guns.” This trend has culminated in the modern era, where the military either procures heavily customized, purpose-built variants of commercial platforms, such as the Mossberg 590A1, or drives the development of entirely new systems, like the Benelli M4 (M1014), to meet stringent reliability and performance standards.

Today, the combat shotgun faces significant doctrinal pressure from the short-barreled rifle (SBR), which offers superior range, capacity, and logistical simplicity for the majority of engagements. Consequently, the shotgun’s role has narrowed, evolving from a primary close-quarters-battle (CQB) weapon to a specialized platform valued for its unique capabilities. These include ballistic breaching, the deployment of less-lethal munitions, and an emerging and highly relevant role in counter-unmanned aerial systems (C-UAS). The future of the combat shotgun lies not in competing with the carbine, but in leveraging its large bore to deliver an increasingly sophisticated array of specialized projectiles, ensuring its enduring, if niche, place in the modern arsenal.

Chapter 1: Inception – From Fowling Piece to Fighting Tool (Pre-1880s)

1.1 The Blunderbuss and “Buck and Ball”: Early Military Scatterguns

The modern combat shotgun’s lineage does not begin with a purpose-built military arm, but with a series of tactical adaptations and civilian tools that established the core concept of a “scattergun” for martial use. The direct ancestor is the blunderbuss, a Dutch invention from the 16th century that saw military service through the 18th century.¹ Characterized by its short, smoothbore barrel and a distinctively flared muzzle, the blunderbuss was engineered for close-range engagements where speed and hit probability were paramount.² The flared muzzle simplified the loading of loose shot and powder, a crucial advantage in the heat of combat, and was believed to widen the spread of the projectiles, making it an ideal weapon for naval boarding actions or for use by cavalry, where targets were fleeting and aim was difficult.²

While the blunderbuss saw some use in the American colonies, a more widespread and uniquely American application of the scattergun principle was the “buck and ball” load.¹ This was not a specific weapon, but a type of ammunition used in standard-issue smoothbore muskets. The load combined a single, caliber-appropriate musket ball with three to six smaller buckshot pellets in a single paper cartridge.⁴ The tactical logic was straightforward: in an era of inaccurate smoothbore firearms and volley-fire doctrine, the buck and ball load dramatically increased the probability of inflicting a casualty with each shot.¹ The musket ball provided the mass for a potentially lethal hit, while the buckshot created a small pattern that could wound or disable other nearby soldiers. This demonstrates that the tactical concept of a combat shotgun—a weapon designed to maximize hit probability in close-quarters combat—was firmly established in U.S. military doctrine long before a dedicated firearm existed to fulfill that role. The load’s effectiveness was famously demonstrated at the Battle of New Orleans in 1814, where it was partially credited for the lopsided casualty rates inflicted upon British forces.¹ The use of buck and ball continued through the American Civil War, primarily by units still equipped with older smoothbore muskets.⁴

1.2 The Coach Gun: America’s First Purpose-Built Defensive Shotgun

As military doctrine was adapting existing muskets, the civilian market was creating the first true purpose-built defensive shotgun: the “Coach Gun”.² These were typically side-by-side double-barreled shotguns, originally designed for sporting, that were modified with their barrels cut down to a handier length of 18 to 24 inches.² They earned their name from their widespread use by stagecoach guards, such as those employed by Wells Fargo, to defend against highwaymen.²

The Coach Gun was a civilian-market solution to a specific tactical problem: defending a moving vehicle against moving assailants at close range. Its short barrels made it maneuverable within the confines of a coach, and the double-barrel action provided two potent shots that could be delivered almost instantaneously, often enough to end an engagement decisively.² While not a standard military-issue weapon, the Coach Gun’s utility was recognized by military forces. During the Civil War, Confederate cavalry units, facing a shortage of purpose-built carbines, frequently armed themselves with these readily available civilian shotguns.² This ad-hoc adoption represented a critical intermediate step in the combat shotgun’s evolution, where a proven civilian defensive tool was integrated into military service out of necessity. It established a precedent that would become a recurring theme: the U.S. military looking to the robust and innovative civilian firearms market to source effective shotgun designs.

1.3 The Impact of Rifling and Metallic Cartridges

The mid-19th century brought two technological revolutions that would definitively shape the future of the combat shotgun by creating its specific tactical niche. The first was the widespread adoption of the rifled musket during the Civil War. Rifling imparted a spin on a single projectile (the Minié ball), dramatically increasing its accuracy and effective range far beyond that of a smoothbore.⁵ This innovation rendered the “buck and ball” load obsolete for general issue, as the spin that stabilized a single bullet caused a chaotic and unpredictable dispersal of buckshot pellets.⁵ This technological divergence forced a specialization of infantry arms: the rifle was now the undisputed king of ranged combat, creating a clear capability gap for a dedicated close-quarters weapon.

The second innovation was the perfection of the self-contained metallic cartridge.⁴ Early shotguns, like muskets, were muzzleloaders. The Civil War saw the introduction of brass-cased shotshells, and by the 1870s, less expensive paper-hulled shells became common.⁴ This development was the final enabling technology for a practical repeating shotgun. Self-contained cartridges made breech-loading mechanisms reliable and fast, paving the way for actions that could cycle multiple rounds from a magazine.⁶ The rise of the rifle did not eliminate the need for the shotgun; rather, by becoming the superior long-range weapon, it carved out the specific niche that only a dedicated, repeating scattergun could fill.

Chapter 2: The Repeating Revolution (1882-1916)

2.1 The First Pumps: Spencer, Roper, and the Birth of a New Action

The technological conditions set in the aftermath of the Civil War—a defined tactical niche and the availability of reliable metallic cartridges—led directly to the invention of the repeating shotgun. The first commercially successful design was not from Winchester or Remington, but from Christopher Spencer, the famed inventor of the Spencer repeating rifle that saw extensive use by Union cavalry.⁷ In 1882, Spencer, in collaboration with Sylvester Roper, patented a slide-action, or “pump-action,” repeating shotgun.⁷

The Spencer 1882 was a groundbreaking, if mechanically complex, firearm. It featured a five-round tubular magazine and a unique top-ejecting mechanism where the breechblock would flip up to eject the spent shell.⁷ The U.S. Army Ordnance Department showed early interest, purchasing 354 of these shotguns between 1886 and 1893.¹² However, their use was limited to non-combat roles, specifically for guarding prisoners, and the weapon was never formally adopted for general service.¹²

The Spencer’s limited military trial highlights a crucial principle in the evolution of military hardware: being first is not sufficient for widespread adoption. The design, while innovative, was expensive to manufacture and was described by some as a “Rube Goldberg invention” due to its complexity.⁹ It successfully established the

concept of a repeating shotgun for military and security use, but its practical limitations left the field open for a more robust, reliable, and economically mass-producible design to ultimately capture the military and law enforcement markets.

2.2 John Browning’s Dominance: The Winchester M1887, M1893, and the Perfected M1897

The task of perfecting the repeating shotgun fell to John Moses Browning, arguably the most influential gun designer in history. His first foray into the field was the Winchester Model 1887, a lever-action design.⁴ This action type was chosen not for its suitability to a shotgun, but at the insistence of Winchester management, who felt the company’s brand was synonymous with lever-action firearms.¹³ Browning himself knew a pump-action would be superior for a shotshell’s ergonomics, and the relative awkwardness of the M1887 in the market soon proved him right.⁴

Winchester eventually relented, and Browning produced the Model 1893, the company’s first pump-action shotgun.⁴ The M1893 was a significant improvement over the Spencer and proved the superiority of the pump-action concept. However, it was almost immediately rendered obsolete by a rapid advancement in ammunition technology: the transition from black powder to more powerful smokeless powder propellants.⁷ The M1893’s metallurgy was only designed for the lower pressures of black powder shells, and its chamber was sized for the older 2 5/8-inch shells.⁷

This external pressure forced Browning to go back to the drawing board, not to create a new weapon, but to refine and strengthen the existing one. The result was the Winchester Model 1897, one of the most iconic and influential firearms ever produced.⁷ The M1897 featured a stronger frame to handle smokeless powder, was chambered for the new 2 ¾-inch shells, and introduced a “take down” design that allowed the barrel and magazine assembly to be easily separated from the receiver for cleaning and transport.¹⁵ It retained the distinctive external hammer of the M1893 and, crucially, lacked a trigger disconnector. This meant that if the trigger was held down, the weapon would fire as soon as the action was closed, a feature that became known as “slam-firing” and provided a surprisingly high rate of fire.¹

The progression from the M1887 to the M1897 is a masterclass in iterative engineering and market adaptation. Browning’s design evolved in response to both ergonomic realities and fundamental shifts in ammunition technology. The M1897 was a success not just because it was a good design, but because it was the right design at the right time, a robust and reliable platform ready for the leap into modern, high-pressure ammunition. It quickly became the standard by which all other pump-actions were judged and found favor with American law enforcement agencies, who adopted short-barreled versions as “Riot Guns”.¹

2.3 Early Operational Use: The Philippine Insurrection and the Rise of the “Riot Gun”

While the Spencer saw limited use guarding prisoners, the M1897’s military baptism by fire came during the Philippine-American War (1899-1902).⁵ In the dense jungles of the Philippines, U.S. troops were engaged in brutal, close-quarters combat with Moro juramentados, warriors known for their fanatical charges with swords and knives.⁵ In these point-blank encounters, the standard-issue.30-06 Springfield rifle and.38 caliber revolvers proved to be inadequate man-stoppers at times.⁴

The U.S. Army procured approximately 200 Winchester M1897s, typically with longer sporting barrels, for use in the conflict.⁵ The shotgun’s massive firepower, delivering a payload of nine.33-caliber 00 buckshot pellets with a single trigger pull, proved to be the decisive answer to the Moro charges.⁴ This combat experience provided the crucial “proof of concept” for the repeating shotgun as a frontline offensive weapon. Its success was witnessed by influential officers, including Captain John “Black Jack” Pershing, who would later command the American Expeditionary Forces in World War I.⁴ Pershing’s forces also employed M1897s during the 1916 Punitive Expedition into Mexico in pursuit of Pancho Villa.¹

This battlefield validation cemented the shotgun’s role in the American military psyche. When the U.S. faced the similar tactical problem of clearing confined trenches in Europe, the institutional memory of the M1897’s effectiveness in the Philippines directly led to its large-scale procurement and deployment.

Chapter 3: Forged in the Trenches – The World Wars (1917-1945)

3.1 The “Trench Broom”: The M1897 and M1912 in WWI

The static, brutal nature of trench warfare on the Western Front in World War I presented a tactical environment for which the shotgun was almost perfectly suited. The narrow, zig-zagging trenches rendered the long range and precision of standard-issue bolt-action rifles, like the M1903 Springfield, largely irrelevant and cumbersome.⁴ Engagements were often measured in feet, not yards.

Recalling the weapon’s effectiveness in the Philippines, General Pershing requested that shotguns be procured for the American Expeditionary Forces.⁵ The primary weapon acquired was the Winchester Model 1897. However, with Winchester’s production capacity strained by rifle contracts, the U.S. military also procured thousands of other models, including the Remington Model 10 and Winchester’s newer, more refined Model 1912.⁵ The Model 1912, designed by Winchester engineer T.C. Johnson, was an evolution of the M1897 that featured a stronger, enclosed receiver and an internal hammer, making it less susceptible to the mud and debris of the trenches.⁷

Both the M1897 and M1912 were issued in “Trench Gun” configuration. This typically meant a 20-inch, cylinder-bore barrel for maximum shot spread at close range.⁷ Their ability to be “slam-fired” allowed a soldier to hold down the trigger and fire a round each time he worked the pump, unleashing a devastating volley of fire that could sweep a trench clear of defenders, earning the weapon the moniker “Trench Broom”.¹ In the confined, linear battlespace of a trench, the shotgun’s perceived weakness—its limited range—became irrelevant, while its strengths—maneuverability, massive short-range firepower, and high rate of fire—made it the ideal offensive tool for trench raiding and clearing operations.⁵

3.2 Tactical Imperatives: Heat Shields, Bayonet Lugs, and the German Protest

To adapt these commercial shotgun designs for the rigors of combat, several key modifications were made. A perforated steel heat shield was fitted over the barrel to allow a soldier to maintain a firm grip without being burned during the rapid fire of a trench assault.² A bayonet lug was also added, allowing the mounting of the long M1917 sword bayonet.⁴ This transformed the shotgun into a formidable weapon for the hand-to-hand fighting that inevitably followed a charge into an enemy trench.

The “Trench Gun” proved so brutally effective that on September 19, 1918, the German government issued a formal diplomatic protest to the U.S., claiming that the use of shotguns with buckshot violated the 1907 Hague Convention’s prohibition on weapons “calculated to cause unnecessary suffering”.⁵ The Germans threatened to execute any American soldier captured in possession of a shotgun or its ammunition.⁵

The U.S. government, under Judge Advocate General and Secretary of State Robert Lansing, formally rejected the protest. The American response noted that the buckshot projectiles were not designed to expand or flatten in the body and pointed out the hypocrisy of the complaint coming from a nation that had introduced chemical warfare and flamethrowers to the battlefield.⁵ The U.S. threatened swift reprisals against German prisoners if the threat of execution was carried out, and the Germans subsequently backed down.⁵ While legally unfounded, the German protest serves as the ultimate testament to the weapon’s tactical and psychological impact. The fear it instilled in enemy soldiers was a force multiplier, cementing the Trench Gun’s legendary status in military history.

3.3 Ammunition in Crisis: The Failure of Paper Hulls and the Shift to Brass

Despite the shotgun’s mechanical reliability and tactical effectiveness, the system had a critical Achilles’ heel: its ammunition. The standard shotshells of the era were constructed with paper hulls, which were susceptible to moisture.¹ In the perpetually damp and muddy conditions of the Western Front, these paper shells would swell, making them difficult or impossible to chamber, and would often tear upon extraction, jamming the weapon.¹ This systemic failure could render a soldier’s weapon useless at the most critical moment of an assault.

The problem became so acute that troops would attempt to cycle every round they carried through their weapon before a patrol to ensure it would fit, a practice that often deformed the shells further.²⁸ The ordnance department recognized the issue and contracted for the production of shotshells with solid brass casings, which were impervious to moisture.¹ However, these robust shells were produced late in the war and arrived in France just before the Armistice, seeing little, if any, combat.²⁸ This crisis demonstrated a crucial lesson: a weapon system is only as reliable as its ammunition. The failure to provide ammunition suited to the operational environment nearly negated the advantages of the firearm itself, a lesson that would have to be relearned a generation later.

3.4 WWII and the Pacific Theater: Jungle Warfare and New Models

In World War II, the combat shotgun was once again called into service, finding a new niche in the dense jungles of the Pacific Theater.² The U.S. Marine Corps, in particular, found the shotgun to be an ideal weapon for the vicious, close-range fighting characteristic of island-hopping campaigns against Japanese forces.⁷ The close confines of jungle trails and the need to clear fortified bunkers and caves mirrored the tactical challenges of the trenches, and the shotgun’s devastating short-range firepower was again invaluable.¹⁷

The venerable Winchester M1897 and M1912 trench guns were taken from armories and re-issued for service.¹ To meet the massive demand of a global war, the U.S. military also procured several new models of pump-action shotguns. These included the Ithaca Model 37, a hammerless, bottom-ejecting design based on an earlier John Browning patent, and the Stevens Models 520-30 and 620A.⁷

The logistical inertia of the military establishment led to a repeat of the ammunition crisis from WWI. The initial issue of ammunition was again commercial paper-hulled buckshot, which failed predictably in the humid, tropical conditions of the Pacific.¹ This forced the Ordnance Department to once again procure all-brass shotshells. On March 29, 1945, this was finally standardized as the “Shell, Shotgun, Brass, 12-Gauge, No. 00 Buck, M19”.²⁸

World War II also saw the first large-scale procurement of semi-automatic shotguns by the U.S. military. These were primarily the Remington Model 11 and the Savage Model 720, both of which were licensed clones of the Browning Auto-5.⁷ However, at this stage, the long-recoil action of these semi-automatics was not considered reliable enough for the rigors of frontline combat. Their use was largely confined to stateside roles, such as guarding military installations and training aerial gunners, who would practice leading targets by shooting clay pigeons.⁷ This limited adoption showed an institutional interest in the potential of a self-loading shotgun, but a lack of confidence in the existing technology for combat deployment.

Chapter 4: The Cold War Crucible (1946-1980s)

4.1 A Motley Arsenal in Vietnam: Legacy Systems Meet New Contenders

The jungles of Southeast Asia during the Vietnam War created another ideal environment for the combat shotgun. Its effectiveness in breaking ambushes on dense jungle trails and for providing overwhelming firepower during clearing operations in villages and tunnel complexes led to its widespread use.¹

At the outset of the conflict, the U.S. military’s inventory consisted largely of refurbished World War II-era trench guns, primarily the Winchester Model 12 and Stevens M520-30.²¹ As the war escalated and the need for more shotguns grew, the procurement strategy shifted away from the expensive, heavily machined trench guns of the past. Instead, the military turned to acquiring large quantities of commercially available, less expensive “riot guns”.³⁴

This led to a diverse and non-standardized mix of shotguns in the field. The most widely procured model was the Stevens Model 77E, with over 60,000 purchased.³⁵ Many of these were supplied to the Army of the Republic of Vietnam (ARVN), and to accommodate the smaller stature of Vietnamese soldiers, they were often fitted with shorter stocks and rubber recoil pads—the first U.S. combat shotgun to feature such a pad.³⁵ Other significant models procured included the Ithaca Model 37, which became a favorite of U.S. Navy SEALs, and the Winchester Model 1200, a modern design with an alloy receiver intended to replace the venerable Model 12.²¹ This off-the-shelf procurement strategy reflected the urgent operational needs and asymmetric nature of the conflict, prioritizing speed and cost-effectiveness over standardization.

4.2 The Rise of the Modern Pump-Action: The Remington 870 Enters Service

A pivotal development during this period was the military’s adoption of the Remington Model 870. Introduced to the civilian market in 1950, the 870 was designed from the ground up for modern, efficient mass production. It featured a receiver machined from a solid billet of steel, dual action bars to prevent binding, and a simple, robust design that quickly made it a commercial success, supplanting the more expensive Winchester Model 12.⁴

In the 1960s, the U.S. government began purchasing thousands of Model 870 riot guns for use in Vietnam by the Army, Air Force, and Marine Corps.³³ The USMC, seeking a more specialized weapon, issued requirements that led to the adoption of the Model 870 Mark 1 in 1966.³³ This variant was a significant step toward the modern tactical shotgun, featuring an extended magazine tube that brought its capacity to eight rounds (

7+1), a 21-inch barrel with rifle sights, and an adapter to mount the M7 bayonet used on the M16 service rifle.³³

The adoption of the 870, particularly the Mark 1 variant, marked a turning point. It represented the military’s embrace of a platform whose reliability and design had been proven in the competitive civilian market. Furthermore, the move to standardize accessories like the bayonet with the main service rifle indicated a more integrated approach to small arms logistics. The 870’s combination of reliability, affordability, and modern manufacturing set the new standard for tactical pump-action shotguns.

4.3 Specialized Tools for Special Warfare: Modifications and Experimental Ammunition

The unique challenges of special operations in Vietnam spurred significant innovation in shotgun technology. U.S. Navy SEALs, operating deep in the Mekong Delta, developed a particular affinity for the Ithaca Model 37.⁷ Its bottom-loading and ejecting port was a major advantage in the muddy, debris-filled jungle environment, as it offered fewer openings for foreign matter to enter the action compared to side-ejecting designs like the 870.⁷ The Ithaca’s ability to be slam-fired was also highly valued for breaking contact in a sudden ambush.²¹

To further enhance the shotgun’s effectiveness in this role, SEALs and other units began using specialized muzzle devices, most notably the “duckbill spreader”.³⁵ This was a flared choke that caused the buckshot pattern to spread horizontally, creating a wide, scythe-like field of fire ideal for engaging multiple targets in a linear ambush.⁴¹

This era was also a laboratory for ammunition development. The military experimented with flechette rounds, which replaced traditional lead pellets with a cluster of small, fin-stabilized steel darts.²⁸ The theory was that the more aerodynamic flechettes would retain velocity better, increasing effective range and improving penetration through the dense jungle canopy and foliage.⁴² While the range was indeed extended, troops found that the lightweight darts lacked the terminal effectiveness and stopping power of conventional buckshot, and they were never widely adopted.²⁸ The development of these specialized modifications and ammunition types marked a conceptual shift, treating the shotgun not as a single-purpose weapon, but as a versatile platform that could be adapted for highly specific mission requirements.

4.4 The Post-War Police Standard: The 870 and Mossberg 500 Dominate Law Enforcement

In the decades following the Vietnam War, the combat shotgun’s evolution was driven primarily by the American law enforcement market. The two platforms that came to dominate this space were the battle-proven Remington 870 and a new competitor, the O.F. Mossberg & Sons Model 500, introduced in 1961.³

The Mossberg 500 was designed as a direct, lower-cost alternative to the 870. Key design differences included a lightweight aluminum alloy receiver (the 870’s is steel) and a tang-mounted safety on top of the receiver, which is naturally ambidextrous, as opposed to the 870’s cross-bolt safety behind the trigger.³⁷ The combination of reliability, ergonomic features, and affordability made the Mossberg 500 and Remington 870 the ubiquitous police shotguns, found in the trunks of patrol cars and the armories of SWAT teams across the nation.⁴⁴

This widespread adoption by law enforcement created a massive and stable market that, in turn, fueled a feedback loop of development. Police requirements for enhanced durability, simple operation under stress, and the ability to mount accessories like rifle sights, side-saddle shell carriers, and weapon lights led manufacturers to create dedicated “Police” and “Tactical” variants of their shotguns.⁴⁶ This continuous refinement in the law enforcement crucible perfected these platforms, hardening them for heavy-duty use. When the military next sought a new pump-action shotgun in the 1980s, it would be these highly evolved tactical models, not their sporting cousins, that would form the basis for the next generation of combat shotguns.

Chapter 5: The Tactical Renaissance (1980s-Present)

5.1 Standardization and Refinement: The Mossberg 590A1 Becomes the Military’s Pump-Action

Following the Vietnam War, the U.S. military’s shotgun inventory was a mix of aging WWII-era weapons and various commercial models procured in the 1960s. In the 1980s, a push for standardization led to a formal competition to select a single, robust pump-action shotgun for all branches of service.⁴⁷ The requirements were codified in MIL-SPEC 3443E, a brutal torture test that included firing 3,000 rounds of full-power buckshot with no more than two malfunctions.⁴³

Mossberg submitted its Model 500, but the standard commercial version, with its polymer trigger guard and safety button, failed to pass the test.⁴³ In a direct response to the military’s requirements, Mossberg engineered a new, purpose-built variant: the Model 590.³⁷ To meet the final, most stringent requirements of the Navy, this was further refined into the Model 590A1.⁴³ The 590A1 is a heavily reinforced weapon, featuring a thick-walled heavy barrel designed to resist bending or damage (a specific Navy request for use around heavy steel ship hatches), a metal trigger group, a metal safety, an extended magazine tube, and a bayonet lug.⁴³

The Mossberg 590A1 is the only pump-action shotgun ever to pass the MIL-SPEC 3443E test and was subsequently adopted as the standard-issue pump-action shotgun of the U.S. Armed Forces.⁴⁷ This marked a return to the philosophy of the WWI “Trench Gun”—instead of simply adopting a commercial product, the military’s demanding specifications drove the creation of a specific, purpose-built military model. The 590A1 represents the apex of the military pump-action shotgun’s development, a platform co-designed by the user to withstand the worst imaginable conditions of combat service.

5.2 The Semi-Automatic Ascendant: Benelli and the Gas-Operated M4 (M1014)

While the pump-action was being perfected, semi-automatic shotgun technology was making significant advances. The Italian firm Benelli Armi S.p.A. became a market leader with its innovative and highly reliable inertia-driven operating system, featured in tactical shotguns like the M1 Super 90 and the unique dual-mode (selectable pump-action or semi-auto) M3.⁴⁹

In 1998, the U.S. Army Armament Research, Development and Engineering Center (ARDEC), with the Marine Corps as the lead service, issued a solicitation for a new 12-gauge semi-automatic combat shotgun.⁵⁴ The requirements were demanding, calling for extreme reliability across a range of ammunition types and environmental conditions.⁵⁴ In response, Benelli developed an entirely new operating system for its entry, the M4 Super 90. This system, called “ARGO” (Auto-Regulating Gas-Operated), uses two short-stroke gas pistons located just forward of the chamber to cycle a rotating bolt.⁵⁴ The design is simple, self-cleaning, and proved to be exceptionally reliable.

In trials at Aberdeen Proving Ground, the Benelli M4 prototype (designated XM1014) exceeded all requirements, including passing an endurance test of 25,000 rounds without the replacement of any major components.⁵⁴ In 1999, it was officially adopted as the M1014 Joint Service Combat Shotgun (JSCS), with the first units delivered to the U.S. Marine Corps.⁵⁵ The adoption of the M1014 was a landmark event. It signified that semi-automatic technology had finally achieved a level of reliability sufficient for general-issue, frontline military use, effectively closing the decades-long reliability gap with the pump-action. The M1014 delivered a weapon that combined the ruggedness of a combat-grade firearm with a higher rate of fire and reduced felt recoil, representing a true generational leap in combat shotgun capability.

5.3 The Era of Modularity: Picatinny Rails, Optics, Lights, and Adjustable Stocks

The late 1990s and the subsequent Global War on Terror (GWOT) ushered in the era of modularity for military small arms, and the shotgun was no exception. The need for 24-hour operational capability in complex urban environments demanded that weapons be adaptable and capable of mounting accessories like optics, illuminators, and lasers.⁵⁸

The Benelli M1014 was designed from its inception with this philosophy in mind. It was the first standard-issue shotgun to feature an integral MIL-STD-1913 Picatinny rail on top of the receiver, allowing for the easy mounting of red dot sights like the Aimpoint CompM2 or Trijicon ACOG, while still permitting the use of its robust ghost-ring iron sights.⁵⁴ It also featured a telescoping stock, allowing the user to adjust the length of pull to accommodate body armor or for use in confined spaces.⁵⁴

This trend quickly spread. The U.S. Army Special Forces Groups procured “Military Enhancement Kits” for their existing Mossberg 500s, which included collapsible stocks, forend and receiver rail systems, and specialized breaching barrels.⁴³ The civilian and law enforcement markets, which had long driven accessory development, exploded with options. Companies like SureFire developed integrated weaponlight forends, and a vast aftermarket of tactical stocks, shell carriers, and other rail-mounted accessories became available for the popular Remington 870 and Mossberg 500/590 platforms.⁴⁶ The integration of the Picatinny rail marked a paradigm shift, transforming the combat shotgun from a static, iron-sighted firearm into a dynamic and highly adaptable weapon platform.

5.4 The Shotgun as a “System”: Underbarrel Launchers and Specialized Munitions

The most significant doctrinal evolution for the modern combat shotgun has been its transformation from a primary weapon into an ancillary tool integrated with a soldier’s main service rifle. The operational reality is that carrying both a rifle and a separate shotgun is heavy and inefficient, yet the shotgun’s unique capabilities—namely ballistic breaching and the use of less-lethal munitions—remain essential.¹

The first attempt to solve this problem was the Knight’s Armament Company (KAC) Masterkey, which consisted of a shortened Remington 870 shotgun mounted beneath the barrel of an M16 rifle or M4 carbine.⁶² While functional, the system was somewhat cumbersome. The concept was refined and perfected with the M26 Modular Accessory Shotgun System (MASS).¹ Developed in the late 1990s, the M26 is a lightweight, straight-pull bolt-action shotgun that feeds from a detachable box magazine. It can be mounted under an M4 carbine like the M203 grenade launcher or can be quickly detached and fitted with a pistol grip and stock to be used as a standalone weapon.⁶²

The M26 was formally adopted by the U.S. Army and began replacing dedicated M500 breaching shotguns in 2010.⁶² Its adoption codifies a new doctrine: the carbine is the primary tool for engaging the enemy, while the shotgun serves as a mission-enhancing accessory for specialized tasks. The shotgun’s value is no longer measured solely by its ability to fire buckshot, but by its function as a versatile “launcher” for a wide array of specialized projectiles, from frangible breaching slugs to rubber pellets and bean bag rounds.⁴²

Chapter 6: The Future of the Combat Shotgun

6.1 The Carbine Question: Doctrinal Debate and the Niche Role of the Modern Shotgun

The future role and prevalence of the combat shotgun are subjects of intense doctrinal debate, driven primarily by the ascendancy of the modern short-barreled rifle (SBR) and carbine. For the majority of tactical scenarios, a carbine like the M4A1 offers significant advantages over a shotgun. These include a much higher magazine capacity (30 rounds vs. 5-9), a longer effective range, superior accuracy, negligible recoil, and ammunition that is significantly lighter and less bulky, allowing a soldier to carry more rounds.⁶⁶ Furthermore, a single ammunition type simplifies logistics.

The shotgun’s advantages are now confined to a very specific and narrow niche. Its primary strength remains its devastating terminal effectiveness at extremely close ranges (typically inside 25 yards), where a single load of 00 buckshot can deliver overwhelming trauma.⁶⁶ However, its most critical and enduring advantage is its versatility as a launcher for specialized munitions that a rifle cannot fire, such as breaching rounds and less-lethal projectiles.¹

The debate is largely settled: the carbine has won as the superior general-purpose individual weapon for the modern soldier. The shotgun is therefore not obsolete, but its role has been redefined. Its survival and future relevance are contingent on its ability to perform specialized tasks that carbines cannot. The shotgun’s future is not to compete with the carbine, but to serve as a complementary tool for specialists.

6.2 New Threats, New Roles: Anti-Drone Applications and Advanced Breaching

As the shotgun’s traditional CQB role narrows, new threats on the modern battlefield are creating new missions for the platform. The most prominent of these is the role of a counter-unmanned aerial system (C-UAS) weapon.⁷⁰ The proliferation of small, inexpensive, and highly maneuverable commercial drones used for reconnaissance and to deliver explosive payloads presents a significant threat that can be difficult to counter with rifle fire.⁷⁰

This new tactical problem is functionally identical to the shotgun’s original purpose: hitting small, fast-moving aerial targets. The wide pattern of shot greatly increases the probability of hitting a drone compared to a single rifle bullet.⁷⁰ Militaries around the world, observing the conflict in Ukraine, are now actively training and equipping troops with shotguns specifically for this anti-drone role.⁷⁰ This has spurred innovation, with manufacturers developing specialized anti-drone ammunition (such as the Maverick SKYNET round) and dedicated shotgun models, like Benelli’s M4 “Drone Guardian,” often equipped with red dot optics to aid in tracking aerial targets.⁷⁰ This emerging C-UAS mission represents a cyclical return to the shotgun’s roots and ensures its relevance on the 21st-century battlefield.

6.3 Ammunition as the Driver: The Future of Programmable, Guided, and Exotic Projectiles

The next great leap in the combat shotgun’s evolution will likely be driven not by changes to the firearm itself, but by radical advancements in ammunition technology.⁷² The shotgun platform is mature; the pump-action and gas-operated semi-automatic systems are highly refined and reliable. The greatest potential for a paradigm shift in capability lies within the 12-gauge shell.⁷⁴

Future concepts include “smart ammunition” that could integrate microelectronics to allow for programmable airburst capabilities, where a shell could be set to detonate at a specific distance, showering a target behind cover with projectiles. Other possibilities include terminally guided slugs that could make minor course corrections in flight, turning the shotgun into a precision weapon at ranges previously unimaginable.⁷⁴ Further refinement of existing exotic rounds, like the FRAG-12 explosive slug, could provide individual soldiers with a hand-held source of high-explosive firepower.⁴² The development of magazine-fed shotguns, such as the Mossberg 590M and various commercial AR-style designs, is a direct enabler of this future, as detachable magazines allow a user to quickly switch between different types of advanced munitions to match a tactical situation.⁶³ If the shotgun’s future is as a specialized launcher, then the “intelligence” will reside in its payload.

6.4 Concluding Analysis: The Enduring Relevance of the Close-Quarters Dominator

The history of the American combat shotgun is a story of continuous adaptation. From the improvised “buck and ball” loads of the Revolution to the purpose-built “Trench Brooms” of WWI, the off-the-shelf riot guns of Vietnam, and the modular, systems-integrated platforms of today, the shotgun has consistently evolved to meet the demands of the battlefield.

While it will likely never again be the widespread primary combat arm it once was, the shotgun is far from obsolete. Its role has been refined and concentrated, focusing on the tasks where its unique attributes provide an undeniable advantage. As a ballistic breaching tool, a platform for less-lethal force, and an emerging counter-drone system, its utility is secure. The potential for future ammunition technologies to further expand these capabilities is immense. The combat shotgun has proven to be a remarkably resilient and adaptable tool of warfare. For the violent, close-range problems that have defined conflict for centuries, and for the new challenges of the modern era, the raw, decisive power of the scattergun remains an enduring and relevant solution.

Appendix: Summary Timeline of Noteworthy U.S. Combat Shotguns

Model Name/Designation	Introduction Year	Gauge	Action Type	Capacity (Standard)	Key Features / Modifications	Primary Conflicts / Users
Spencer 1882	1882	12	Pump-Action	5	First successful pump-action; complex top-eject mechanism.7	U.S. Army (Prison Guard Use) 12
Winchester M1897 “Trench Gun”	1897	12	Pump-Action	5+1	External hammer; slam-fire capable; adapted with heat shield and M1917 bayonet lug.1	Philippine Insurrection, WWI, WWII, Korea, Vietnam 7
Remington Model 10-A “Trench Gun”	1908	12	Pump-Action	5+1	Hammerless; bottom-eject; adapted with wooden handguard and M1917 bayonet lug.7	WWI 5
Winchester M1912 “Trench Gun”	1912	12	Pump-Action	5+1	Hammerless internal action; slam-fire capable; adapted with heat shield and M1917 bayonet lug.7	WWI, WWII, Korea, Vietnam 7
Remington Model 11 “Riot Gun”	1905	12	Semi-Auto (Long Recoil)	4+1	Browning Auto-5 clone; primarily used with 20-inch barrel for guard duty and training.7	WWII (Rear Echelon/Training) 32
Ithaca Model 37 “Trench/Riot Gun”	1937	12	Pump-Action	4+1	Hammerless; bottom-eject; slam-fire capable; used as riot gun and trench gun.7	WWII, Korea, Vietnam (USMC, SEALs) 7
Stevens M520-30 / M620 “Trench Gun”	c. 1942	12	Pump-Action	5+1	Takedown designs based on Browning patents; adapted with heat shield and bayonet lug.7	WWII, Korea, Vietnam 7
Stevens Model 77E “Riot Gun”	c. 1963	12	Pump-Action	5+1	Most numerous shotgun of Vietnam War; often had shorter stock for ARVN forces.35	Vietnam (U.S. Army, USMC, ARVN) 35
Remington M870 Mk 1	1966	12	Pump-Action	7+1	Extended magazine tube; 21″ barrel with rifle sights; M7 bayonet lug.33	Vietnam (USMC) 33
Mossberg 590A1	1987	12	Pump-Action	8+1	Heavy-walled barrel; metal trigger group and safety; passed MIL-SPEC 3443E.43	Post-Vietnam Standardization, GWOT, Present (All Branches) 1
Benelli M4 / M1014 JSCS	1999	12	Semi-Auto (Gas)	7+1 (Mil)	ARGO gas system; collapsible stock; integral Picatinny rail.54	GWOT, Present (USMC, All Branches) 55
M26 MASS	2010	12	Bolt-Action (Straight-Pull)	3 or 5	Underbarrel or standalone configuration; detachable box magazine.1	GWOT (U.S. Army), Present 1

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