Gustavus Adolphus, a key reformer of armed forces in the 17th century, was crowned king of Sweden at age 17. His country was poor and sparsely populated, but already the ambitious young “Lion of Midnight” (that is, of the North) intended to enrich it with new lands and looted wealth. The only way to do that was by war, so he set out to reform the army. He soon proved to be a superb reformer and administrator within Sweden, and later emerged as an even more able strategist and general in Germany. Over his first decade as king, he transformed the army into a national force and built up the navy to protect his supply route to Poland and Germany. As Gustavus modernized the weapons, drill and fighting techniques of the Swedish army, he also professionalized it, by shifting recruitment away from a traditional levy of ill-trained peasants raised locally to create a national army of well-trained regulars secured for long-term service by conscription. He took the best Dutch innovations out of the waterlogged, compact and canalized environment of the Netherlands to maximize their revolutionary potential on the broad battle plains of Poland and Germany, where a war of maneuver was more likely to lead to field battles and more able to achieve success. Like Maurits and other Dutch reformers, he newly emphasized drill and infantry discipline, centered on learning volley and double-volley fire. In disposition for battle he deployed by brigades, freeing his troops from the old infantry blocks, reorganizing into flexible and more linear formations. Thinning was achieved at some defensive cost, as lines exposed flanks when moving in ways that a pike square of 50 × 50 or so ranks and files did not. The trade-off was worth it: all this cleared the way for Sweden’s ascent into the ranks of the Great Powers, to intervention in the Thirty Years’ War for Swedish gain and the Protestant cause.
Before he left for Germany, Gustavus also experimented with shortening and thinning the extremely heavy barrels of his cumbersome Murbräcker (“wall-breaker”) large-caliber siege guns. Murbräcker barrels were often inscribed with boasts of their special prowess in knocking down fortifications, praise for their royal owners or religious pieties that dominated Swedish (and German) service. Gustavus was not impressed. He trimmed barrel length to reduce haul-weight, as well as the number of horses or oxen and wagons of fodder needed to move his siege guns. He also cast innovative small-caliber cannon called “leather guns.” These were cast from iron, but lined with brass or copper and reinforced with alloy. Barrels were bound with wire and rope splints, then wrapped in canvas secured by wooden rings. Hard leather was nailed to the exterior. They weighed about 600 pounds, making them highly mobile as well as cheap. They became famous, but were not a true success. All-iron casting proved superior in the end, leading even Gustavus to prefer small regementsstycke (“regimental guns”) that then became standard. By around 1640, leather guns were retired by Sweden in favor of all-iron cannon, and only used after that by mercenaries returning to fight in the Wars of the Three Kingdoms (or English Civil Wars) in Scotland and Ireland. His less famous but more successful regimental guns were standardized one-and-a-half- and three-pounders. Although cast all in iron, they were light enough to be pulled by one or two horses, using a two-wheeled carriage that allowed off-road maneuvers before battle and repositioning of the artillery during battle, something no other army could then achieve. These excellent small cannon also had rates of fire exceeding the top rates of good musketeers. They gave Swedish armies more maneuverable firepower in battle than any other army of the time.
Gustavus understood the role of shock in combat, of delivering a stunning, smashing attack directly and bluntly into an enemy with the weight and force of a whole military unit. He maximized it by double-volley fire by infantry, hard charges by cavalry, and a range of big guns as well as small leather guns and regimental pieces. His light guns were supported by less mobile heavies standardized at 6-, 12- and 24-pound calibers. He also standardized charges and shot for each caliber. Powder was bagged in measured sacks, improving reload times, rate of fire and repeat-fire accuracy. Cannon traveled with the siege train hauled by large teams of draught animals, or moved by barge, the army marching down a river’s shore alongside the floating guns just as Maurits of Nassau had moved his big guns in Flanders. Other generals left their largest guns to follow their armies in cumbersome land-bound siege trains, intending to use them to batter forts or city walls. Their oversized and immobile cannon could be positioned just once in a field fight, at the start of a battle. Most enemy cannon were too big to reposition as the Swedes shifted out of the line of fire, leaving the big enemy guns uselessly misplaced while repositioning their own lighter field pieces. Gustavus made sure his light guns moved with his infantry and cavalry, always ready for deployment. In battle, he positioned the small-caliber regimental guns ahead of the infantry, moving them as his foot soldiers moved, uniquely able to shift position to cover a suddenly exposed flank, or sometimes to spring a trap with a battery deliberately hidden by a cavalry or infantry screen.
Gustavus adopted wheel-lock muskets that were much smaller and lighter than the heavy-caliber Spanish musket, a matchlock that required two men or a forked rest to fire. He greatly increased the proportion of musketeers to pikers in the ranks, enhancing infantry punching power. He even shortened pikes to 11 feet from the more common 18 to 21 feet, making his last pikers as light and maneuverable as the musketeers they protected from enemy horse. Three or four brigades formed a flexible, articulated, extended battle line. Each brigade subdivided into three squadrons of about 500 each, providing even more flexibility and chance to maneuver. Whenever flanked, Swedish infantry quickly articulated to bring musket volleys to bear from a newly right-angled line, along with easily repositioned one-and-a-half- or three-pounder guns. Reducing firing ranks to six and using double-volleys meant that all interior and back ranks had clear fields of fire, while each brigade was confident that half its number always stood ready with muskets loaded. Putting the regimental guns forward added killing range and firepower in mobile attack and defense.
Gustavus modeled his cavalry on superb Polish horse units, characteristic of Eastern European warfare but largely unknown in Western Europe. He stripped armor from men and mounts alike, fielding lighter horses and hussar-like cavalrymen dressed in hard leather and simple cloth. He replaced with sabers and lances the wheel-lock pistols used to such little effect in the tactic called caracole. That was a wheel-lock pistol-and-cavalry tactic prevalent in Western Europe in the 16th century, especially among German cavalry (Ritter). It had some use against units of pikers alone, but almost none against musketeers protected by pikers. The caracole abandoned the physical and psychological shock effect of the horse charge with lance or saber in favor of riding in short columns at a trot, one by one or two by two, up to a pike-and-musket hedge, discharging pistols (each rider carried a brace), then whirling away to reload at a safe distance before returning to fire weapons a second or third time. Since pistols had a range barely past ten feet, if that, and the average pike was 18–24 feet before Gustavus’ reforms, human nature encouraged shooting from outside effective range. The caracole thus presented great danger to attacking cavalry but offered little offensive punch against musket infantry. Trouble mounted, or rather dismounted rather violently, when aggressive infantry with hooked pikes or halberds attacked, or a musket volley hurtled lead at too carefully approaching horsemen.
Gustavus wanted shock restored, so horses in the Swedish cavalry were retrained to canter and gallop rather than caracole trot toward the enemy, while their riders were told to pull sabers and use lances, to reinstate the fearful cavalry charge of old. He thereby returned to the horse arm its ancient role in providing shock, but did it by favoring light cavalry speed over heavy cavalry mass. This reform took advantage of the widely noted Swedish martial ferocity and his cavalry’s desire to pursue a defeated enemy. The advantage was immense as long as other cavalry still deployed in overly dainty and ineffectual long columns to perform the caracole, only to be easily dispersed. In battle, his horse always deployed on the wings, where its first obligation was to block enemy cavalry from taking offensive action. Only secondly was it to exploit gaps or exposed flanks and any opportunity to attack created by the superior firepower of his hard-punching infantry, firing double volleys, and his mobile artillery occupying the flexible center of his line of battle.
Gustavus stressed pre-battle preparation and deliberation, but also an eager offensive spirit that sought to carry war to the enemy. He was among the first to employ recognizably modern techniques of combined arms by coordinating attacks by mutually supporting infantry, artillery and cavalry units. Similarly, he pioneered fire-and-movement tactics, while reviving the ancient principle of concentration of force at a chosen point of local superiority. The weight (and shock) of a Swedish attack came from the infantry and field artillery. Batteries of little guns peppered an enemy square or line with canister at intimate ranges, punching bloody gaps in opposing ranks. Then infantry closed to maximize the effect of their double musket volleys. After firing two or three salvoes at most, front ranks charged with short pikes level and muskets reversed and used as clubs. Through all this, three back ranks (countermarched into place) always stood ready to exploit a breakthrough or pivot to defend their brigade’s flanks, or to counterattack if arrayed for defense. Always the cavalry hovered, light and able and lethal. Skilled Swedish armies could do terrible violence to more staid and conservative enemies. It was awful and brilliant all at once.
When Gustavus was done remaking and reforming the Swedish army, it was one of the finest and most deadly of the era: well-drilled and disciplined, infused with a conjoined spirit of martial patriotism and fervent Protestantism, and uniquely able to shift from offense to defense with a battle speed and efficiency unmatched by any other force in Europe. He tested its mettle, and his generalship, in Poland. In 1627, he attacked Danzig. At Dirschau (August 17–18), then in Pomerania but today called Tczew and in Poland, he was seriously wounded in the neck and arm but won the field. This was one of several times where the young king led from the front. He was nearly killed, and was defeated as well, at Stuhm (Sztum) on June 27, 1629, in what is today northern Poland. Gustavus withdrew to recover from his wounds, prepare fixed defenses and reconsider the campaign. The wily éminence rouge in Paris, Cardinal Richelieu, took advantage of the lull to arrange the Truce of Altmark with Poland’s Sigismund III, who agreed to renounce his claim to the Swedish throne. It was 1630, and Gustavus was at last ready to enter the war in Germany, which was going badly for the Protestant princes. His alliance with France gave him yet more incentive: a subsidy of 400,000 thalers annually and a powerful ally on the other side of the Holy Roman Empire. Protestants across Germany and Europe begged him to be their champion. As did Cardinal Richelieu, although he was pursuing secular and monarchical raison d’état for France in open opposition to Catholic Habsburg power in Vienna and Madrid.
Gustavus appeared to be a sincere Lutheran, leading troops in singing hymns as they marched into battle and ordering prayers said twice daily by the whole army under the supervision of pastors he assigned to each brigade. Accepting Richelieu’s mediation of his old dispute with Poland so that he could move into Germany instead, Gustavus took his Swedish version of a 17th-century new model army into the Thirty Years’ War, singing Lutheran hymns along the way. His Nordic blend of piety, drill and black-powder aggression would give his armies unusual discipline and cohesion in combat. Napoleon later compared him to Alexander the Great, naming Gustavus as one of the first of the modern great captains. The comparison seems exaggerated, even if, like Alexander, he would be cut off in the flower of his military prowess, killed leading a wild battle charge in Germany in 1632.
He landed at Peenemünde in July 1630, with just 14,000 men. He had 80 field guns to go along with larger siege cannon. The ratio of nearly 10 artillery pieces per 1,000 men in his army compared to just one cannon per 1,000 men for the Imperials. Despite his reforms, he could only rely on about 10,000 fresh Swedish recruits each year, so around the hard national army core of well-trained Swedes he wrapped mercenaries as he proceeded into Germany. With a smaller war chest than his Imperial foes, he needed even more to make war pay for itself by battening and billeting his army on other people’s estates and cities. He moved deliberately, gathering intelligence, conserving combat power, growing his forces, knowing he did not have strength enough to force the issue all at once. All the same, as the inherently weaker side, Gustavus kept the option of an aggressive battle in his pocket, ready to take it out if opportunity presented.
So began the Swedish intervention in the Thirty Years’ War that was to change its course, turning it away from the Catholic-Habsburg victory that loomed in 1630 toward the confessional stalemate and negotiated secular peace of 1648. Gustavus’ spectacular success in the two years that followed, lasting until his death at Lützen in 1632, arose less from any battlefield tactical genius than from intense advance preparation of the army and from his acute sense of weaknesses in the enemy’s psychology and politics. He exploited flaws he saw in his enemies positions, but not always or even mainly by hard action driven by a coup d’oeil, that quality some great generals have of seeing immediately to the essence of a how a fight will develop, based perhaps on an innate ability to read terrain and position and the balance of available forces. He had that natural commander’s gift, but he waged campaigns more by way of threat and daring maneuvers and long marches. He repeatedly got his army behind the main enemy force, causing Habsburg generals to rush back to defend some important holding or damp down the emperor’s fright in Vienna. It was a variation of old-style war by maneuver by the mercenaries, but always with a sting of battle at the ready should the enemy flag or challenge. Like all superior generals he was flexible in tactics and operations rather than committed to a system, with an eye always on the strategic goal. He would fight battles if needed, but preferred to achieve gains by marching against the enemy’s supplies whenever possible. He used armies to threaten Habsburg political and prestige interests as much as he threatened their hired soldiers and stiff artillery fortresses. He saw battle and maneuver as closely related, not as opposing strategic choices, all one or all the other.
In search of food and fodder Gustavus moved beyond Pomerania, which was already eaten out. He followed the rivers of northern Germany, subjugating and garrisoning towns, securing rearward lines of supply and contributions and putting a territorial buffer between Sweden and its enemies. Then he settled in for the winter, recruiting and training tens of thousands of German (and Scots and Irish and other) mercenaries in his reformed—rather than Reformation—way of war. Winter increased his strength but exacerbated logistics, forcing him onto the road with the spring thaw of 1631. He marched into Brandenburg to feed his army and force its elector to join the war. He ambled south, taking the fortress of Cüstrin (Kostrzyn nad Odrą), then westward to Berlin to reduce the fortress at Spandau. That secured the confluences of the major navigable rivers of north Germany, which he needed in order to shift guns and supplies by barge toward the southern Habsburg heartlands. On April 13, he stormed Frankfurt an der Oder, smashing eight Imperial regiments and slaughtering a third of its 6,400-man garrison in reprisal for earlier Catholic atrocities. With his army shrunken by wounds and illness and the needs of spread-out occupation and resupply, he could not reach or relieve Magdeburg, a major Protestant center under siege by a large Catholic-Habsburg army. Without Gustavus to protect it, Magdeburg’s walls were breached and its population put to the sword, starting on May 20, 1631. Some 20,000 died in a guerre mortelle revenge for resistance, killed by Imperial troops and the allied Army of the Catholic League, led by General Johann Tserclaes, Count von Tilly.
Magdeburg was the worst atrocity of the Thirty Years’ War and became the benchmark for all later 17th-century atrocities, echoing across Europe for decades; the city remained largely a ruin until 1720. At the time, the sack of Magdeburg strengthened Gustavus by raising levels of fear and resolve among Protestants everywhere: pamphleteers kept printing presses rolling with lurid tales and fine etchings of horror. Meanwhile, Gustavus cleared Pomerania of Imperial armies and garrisons, then marched into Saxony, forcing it into the war. Now he was ready to meet Tilly and the Army of the Catholic League in battle. Between July 22 and 28, 1631, he waited for the Catholic League army, blocking the road north at Werben with 16,000 entrenched Swedes. Tilly blundered into the position and attacked with his heavy tercios, twice in six days. Repulsed by firepower from double volleys and regimental guns, Tilly left over 6,000 dead in front of the fieldworks at Werben. He withdrew into Saxony on the twin mission of eating out Gustavus’ new but always reluctant ally and to bind his own army’s wounds while feeding his men with Protestant grain, sheep and wine.