Combined arms
Based on Wikipedia: Combined arms
Here's a battlefield puzzle that has stumped commanders for millennia: your infantry can hold ground, but they're vulnerable to cavalry charges. Your cavalry can crush infantry caught in the open, but they'll be slaughtered if those infantry form a tight defensive square. Your archers can devastate both from a distance, but they're helpless if anyone gets close enough to swing a sword.
Each force has a fatal weakness. Each can be defeated by an enemy who exploits that weakness. So what do you do?
The answer—one of the most consequential ideas in military history—is deceptively simple: you combine them.
The Dilemma That Cannot Be Solved
Combined arms warfare isn't just about having different types of soldiers work together. That's supporting arms, and it's been around since the first human picked up a rock while his friend brandished a stick. Combined arms is something more devious.
The strategist William S. Lind draws a crucial distinction:
Combined arms hits the enemy with two or more arms simultaneously in such a manner that the actions he must take to defend himself from one make him more vulnerable to another. In contrast, supporting arms is hitting the enemy with two or more arms in sequence, or if simultaneously, then in such combination that the actions the enemy must take to defend himself from one also defends himself from the other(s).
Read that again, because it's the crux of everything.
With supporting arms, your enemy has a way out. He can defend against your archers, then pivot to defend against your cavalry, then deal with your infantry. It's hard, but it's solvable.
With combined arms, you've given him an impossible choice. If he spreads out to avoid your artillery, your machine gunners will cut him down. If he bunches up to avoid the machine guns, your artillery will obliterate him. If he hides in trenches from both, your tanks will roll right over him. And if he comes out to fight the tanks, he's back to being exposed to artillery and machine guns.
There is no right answer. That's the point.
An Ancient Solution to a Timeless Problem
Philip II of Macedon figured this out around 350 BCE, and it made his kingdom the most dangerous power in the ancient Mediterranean.
The Greek city-states had spent centuries perfecting the phalanx—a dense formation of heavily armored infantry called hoplites, fighting shoulder to shoulder with overlapping shields and long spears. It was nearly impenetrable from the front. It was also slow, inflexible, and utterly predictable.
Philip didn't try to build a better phalanx. He built a system.
His Macedonian phalanx used even longer spears—the sarissa, some six meters long—which made it even more dangerous to approach head-on. But the phalanx wasn't meant to win battles. It was meant to pin enemies in place, to force them to stand and fight, to hold their attention while something else happened.
That something else was the Companion cavalry, the finest heavy horsemen in the ancient world. While enemy infantry struggled against the bristling wall of spear points, unable to advance, unable to retreat, the cavalry would sweep around the flank and smash into their exposed side or rear.
The infantry created the problem. The cavalry exploited it. Together, they were devastating.
Rome's Evolving Machine
The Roman Republic developed its own approach, one that evolved over centuries of continuous warfare.
The early Roman legion was a layered system of five different troop types. At the front, the velites—lightly equipped young men with javelins—would harass the enemy, testing their formation, forcing them to raise their shields. Behind them came the hastati, the first line of heavy infantry, followed by the more experienced principes. Both fought with the gladius, a short stabbing sword perfect for the close-quarters butchery that Romans excelled at, and the pilum, a heavy javelin designed to bend on impact so it couldn't be thrown back.
If the hastati and principes failed, there were the triarii—older, veteran soldiers who fought as spearmen in a more traditional formation. The saying "it has come to the triarii" became a Roman idiom for a desperate situation.
Finally, there was the cavalry, the equites, used for scouting, pursuit, and protecting the flanks.
Each element had its role. The velites disrupted. The heavy infantry ground forward. The triarii provided the backstop. The cavalry exploited opportunities. It wasn't elegant, but it was relentlessly effective.
When One Arm Isn't Enough
The Battle of Hastings in 1066 demonstrated what happens when one side uses combined arms and the other doesn't.
King Harold's English army had an excellent defensive position atop Senlac Hill. His soldiers formed a shield wall—a dense line of men with interlocking shields, bristling with axes and spears. Against infantry or cavalry alone, it was nearly impregnable.
Duke William of Normandy had archers, infantry, and cavalry. He used all three.
His archers rained arrows on the shield wall, forcing the English to keep their shields raised. His infantry advanced to engage, keeping them locked in place. And when groups of English broke formation—whether to pursue apparently retreating Normans or simply because they couldn't maintain discipline under the relentless pressure—his cavalry ran them down in the open.
The English could have beaten the archers alone. They could have held against the infantry alone. They might have survived the cavalry alone. But all three together, coordinated, created problems faster than Harold could solve them.
The Sheltron's Fate
The Scottish learned this lesson at Falkirk in 1298. Their schiltrons—dense circular formations of spearmen—had proven devastatingly effective against English cavalry at Stirling Bridge the year before. A wall of twelve-foot spears pointing outward made cavalry charges suicidal.
At Falkirk, the English didn't repeat their mistake. They brought archers.
The Scottish spearmen couldn't advance against cavalry without breaking formation. They couldn't disperse without being ridden down. So they stood in their circles and died under a hail of arrows, unable to reach their tormentors, unable to escape them.
Edward I didn't even need to charge. He just had to wait.
The English Solution
The great English victories of the Hundred Years' War—Crécy in 1346, Poitiers in 1356, Agincourt in 1415—reversed this equation with elegant simplicity.
English armies combined dismounted knights with longbowmen. The knights, heavily armored and fighting on foot, formed a solid defensive core. The longbowmen, protected by stakes and the terrain, could shoot down advancing enemies from distances the French couldn't match.
French cavalry couldn't charge the bowmen without first crossing through a storm of arrows. Those who survived found themselves facing dismounted English knights—professional killers perfectly happy to fight on foot. French infantry faced the same problem, only worse, because they had to cross even more ground under fire.
The longbowmen alone would have been vulnerable to a determined charge. The knights alone could have been surrounded and overwhelmed. Together, they were nearly unbeatable on the defensive.
Pike and Shot
The introduction of gunpowder weapons created new possibilities and new problems.
Early firearms were slow, inaccurate, and useless at close range. A formation of musketeers could devastate an enemy at fifty meters but would be helpless against cavalry or pikemen who closed the distance. They needed protection.
Enter the tercio, developed by Spanish commanders in the late fifteenth and early sixteenth centuries.
A tercio combined pikemen and musketeers in a single formation. The pikemen—with their five-meter spears—kept cavalry at bay and provided a hedge against infantry charges. The musketeers, protected by that bristling forest of pikes, could load and fire with relative impunity.
Attack the musketeers and the pikemen would skewer you. Attack the pikemen and the musketeers would shoot you. It was the combined arms principle applied to a single tactical unit.
Japan discovered the same solution independently. At the Battle of Nagashino in 1575, Oda Nobunaga defeated the fearsome cavalry of the Takeda clan by combining ashigaru musketeers with protective palisades and samurai swordsmen. The cavalry couldn't reach the gunners; those who somehow got through the bullets met samurai ready to cut them down.
The Swedish Revolution
King Gustavus Adolphus of Sweden, who reigned in the early seventeenth century, pushed combined arms integration to new depths. Rather than keeping different troop types in separate formations, he mixed them together at lower and lower organizational levels.
He attached teams of "commanded musketeers" directly to his cavalry units, giving horsemen their own integral fire support. He developed light three-pound cannons that could be hauled around the battlefield by just a few men, providing infantry regiments with organic artillery that could keep up with them as they advanced.
This wasn't just tactical innovation—it was organizational revolution. Previous armies had kept infantry, cavalry, and artillery in separate blocks, coordinating them from above. Gustavus built combined arms teams at the regimental level, giving local commanders the tools to respond to battlefield developments without waiting for orders from the top.
Napoleon and the Corps System
By the Napoleonic Wars, combined arms organization had become systematic. The great innovation was the corps—a self-contained force of ten to thirty thousand men that included its own infantry divisions, cavalry brigades, and artillery batteries.
A Napoleonic corps could march independently, fight independently, and survive on its own for extended periods. It wasn't just a collection of different troop types—it was a balanced force capable of any mission. Napoleon could scatter his corps across a wide front during an approach march, knowing that any one of them could hold against enemy attack until the others concentrated for a decisive battle.
The system reached its peak at Waterloo in 1815, where both sides organized their forces into combined arms corps. The battle itself demonstrated both the power and the limitations of the approach. Marshal Ney's famous cavalry charges failed precisely because he didn't bring enough infantry and artillery to exploit any success his horsemen achieved. The French cavalry broke themselves against British infantry squares—squares that might have been shattered by combined cavalry and artillery working together.
Meanwhile, the 27th Regiment of Foot, the Inniskillings, suffered nearly two-thirds casualties because they were exposed to French combined arms in a way most of Wellington's force was not. Positioned in a depression on the forward slope, they couldn't shelter behind the ridge like their comrades. Forced to remain in square against cavalry, they presented a dense target for French artillery. The combination was devastating.
The Trenches and Their Solution
World War I should have been over by Christmas 1914. It lasted four years and killed millions, largely because combined arms tactics had to be reinvented for an age of machine guns, barbed wire, and high-explosive artillery.
The problem was simple to state and seemingly impossible to solve. Machine guns could mow down infantry attacks from hundreds of meters away. Artillery could obliterate any fixed position. Trenches provided protection from both—until someone went over the top.
Attacking was suicide. Defending was stalemate. Millions died in futile offensives that gained meters and lost generations.
The solution, when it finally emerged, was timing.
The creeping barrage coordinated artillery and infantry so precisely that shells fell just ahead of advancing troops—close enough that the defenders couldn't emerge from their bunkers, but moving forward fast enough that the attackers could reach the enemy trenches before the stunned survivors could man their weapons.
Add tanks to break through wire and suppress machine gun nests. Add aircraft to spot targets and strafe reinforcements. The Battle of Cambrai in November 1917 combined all these elements and achieved in hours what previous offensives had failed to accomplish in months.
It wasn't just having tanks, artillery, and infantry. It was coordinating them so tightly that each arm's success depended on the others, and together they created problems faster than defenders could solve them.
Blitzkrieg and Deep Battle
World War II saw combined arms reach a new level of sophistication.
The German blitzkrieg—literally "lightning war"—didn't rely on any single revolutionary weapon. Tanks, aircraft, and motorized infantry all existed before 1939. What German commanders like Heinz Guderian developed was a system for using them together at unprecedented speed.
Dive bombers acted as flying artillery, striking enemy strong points precisely when and where ground forces needed support. Tanks punched through defensive lines at their weakest points. Motorized infantry followed to hold the gaps open and mop up bypassed defenders. Radio communications kept everything coordinated, allowing commanders to shift forces and exploit opportunities faster than their enemies could react.
The Soviets developed their own approach, called deep battle. Rather than simply breaking through enemy lines, deep battle aimed to attack the entire depth of an enemy's military system simultaneously—front-line units, reserves, supply lines, headquarters, everything at once.
Combined arms operations would create breakthroughs. Mobile forces would exploit them, racing deep into enemy territory. Airborne troops might seize key points behind the lines. The goal wasn't just to defeat enemy forces but to paralyze them, to create so many crises simultaneously that no response was possible.
The Marine Air-Ground Task Force
In 1963, the United States Marine Corps formalized a concept that would become its defining organizational principle: the Marine Air-Ground Task Force, or MAGTF.
A MAGTF combined Marine aviation and Marine ground units under a single commander for expeditionary missions. Unlike the Army, which had to coordinate with a separate Air Force, the Marines owned their own aircraft and could integrate air and ground operations at the lowest levels.
This wasn't just bureaucratic convenience. It meant that a Marine battalion commander could count on air support the way an Army officer could count on his mortars—as an organic asset, not a favor from another service. The resulting flexibility made Marine units disproportionately effective for their size.
The Helicopter War
Vietnam transformed American combined arms doctrine in ways that are still being felt today.
The terrain made traditional ground operations nearly impossible. Dense jungle. Mountainous highlands. An enemy who refused to concentrate in targetable formations. American forces adapted by taking to the air.
The helicopter—specifically, the UH-1 Huey and its armed cousins—became the centerpiece of a new kind of combined arms. Troops could be inserted directly into battle by air assault, bypassing the jungle trails and roads that would have made conventional movement suicidally slow. Gunships provided immediate fire support. Helicopters delivered ammunition, food, and medical evacuation faster than any ground convoy could manage.
American infantry in Vietnam saw six times more combat than soldiers in previous wars—not because they were braver, but because they could be transported to and supported in battle so much more effectively. A rifle company supported by helicopters was effectively four times more capable than its paper strength suggested.
The combination of airmobile infantry, helicopter gunships, artillery firing from distant fire support bases, naval forces operating on the rivers, and Air Force close air support created a web of mutually supporting capabilities that proved extremely difficult to counter.
AirLand Battle
The doctrine the U.S. Army developed for a potential World War III in Europe, called AirLand Battle, represented perhaps the most sophisticated articulation of combined arms thinking ever codified.
AirLand Battle, which guided American planning from 1982 into the late 1990s, envisioned ground forces conducting an aggressively mobile defense while air power struck deep into enemy rear areas. The ground forces wouldn't just fight the enemy units in front of them—they would maneuver to shape the entire battle, creating opportunities for air strikes and exploitation.
Meanwhile, aircraft would attack the enemy's second echelon: the reserves, supply columns, and command posts that fed the front lines. By the time those reinforcements reached the battle, they would be depleted, disorganized, and cut off from higher command.
The ground and air components were designed to be synergistic in the deepest sense. Neither could succeed without the other. The ground forces created the conditions for air attacks; the air attacks enabled ground success.
The 100-Hour War
The 1991 Gulf War demonstrated what modern combined arms could accomplish when everything worked.
General Norman Schwarzkopf's campaign against Iraq began with weeks of air attacks—not just bombing, but a systematic effort to blind and paralyze the Iraqi military. Radar sites, communication centers, command bunkers, bridges, supply depots—everything that held the Iraqi army together was systematically destroyed.
When the ground assault came, Iraqi forces were deaf, blind, and starving. They couldn't communicate with their headquarters. They couldn't coordinate responses. They couldn't even see what was coming.
What came was everything at once. Fixed-wing aircraft dropped precision-guided bombs on any position that showed resistance. Attack helicopters hunted tanks. Armored columns swept forward at speeds that would have seemed impossible to commanders from earlier generations—forty to fifty kilometers per hour, the upper limit of what tracked vehicles could sustain.
The ground war lasted one hundred hours. Coalition forces destroyed an army that was, on paper, one of the largest in the world.
The Modern Mix
Today's combined arms teams are more sophisticated than anything Philip of Macedon could have imagined, but the principle remains unchanged.
A modern armored division combines mechanized infantry, tanks, artillery, reconnaissance units, air defense systems, drone support, close air support, and attack helicopters—all coordinated by a unified command structure with real-time communication capabilities.
But it goes further than that. Ground forces can now call on space-based reconnaissance satellites, cyberwarfare units attacking enemy communications, electronic warfare systems jamming radars and disrupting command networks, naval bombardment from ships hundreds of kilometers away.
The mix can be pushed down to remarkably low levels. A tank company might be attached to an infantry battalion. Drone operators might work directly with a rifle squad. The boundaries between branches blur as the need for integration extends to the smallest units.
The Eternal Dilemma
What makes combined arms so enduring isn't technological—it's logical.
Every military capability has counters. Every defense has weaknesses. Any force that relies on a single arm, no matter how excellent, gives its enemy a problem that can be solved.
Combined arms denies that solution. It presents the enemy with simultaneous, interlocking threats that cannot all be countered at once. Defend against one and you expose yourself to another. There is no optimal response, only a choice between different flavors of disaster.
Philip of Macedon understood this. So did the Roman consuls, the Norman dukes, the English kings, the Napoleonic marshals, the World War generals. The weapons change. The vehicles evolve. The communications advance. But the fundamental insight—that forces combined correctly can achieve what no single force could accomplish alone—remains as relevant today as it was two and a half thousand years ago.
It is, perhaps, the closest thing to a universal law that warfare has ever produced.