Spain’s partial recovery in 1647–8 limited what France could do in the Empire, where the exact outcome of the war remained unclear. It was obvious the emperor was losing, but even a local victory could still upset the two crowns at Westphalia. They had gained ground, but still lacked a decisive preponderance and reports that they outnumbered the imperial and Bavarian forces two-to-one at the end of 1648 are exaggerated.
The proportion of Swedish nationals in that country’s army was now much higher, at 18,000 out of 63,000, due to mistrust of the Germans. A major effort was made to improve the cavalry as these represented 22,000 of the 37,500 field troops. The eleven German cavalry regiments that defected from Turenne were reorganized into four larger units, while 14,000 horses were rounded up across Lower Saxony as remounts. The ratio of horse to foot was now the reverse of that in 1618. Logistical reasons continued to propel this, but the Swedes also needed to be mobile to assist their negotiators in Westphalia.
Nearly a third of the garrison troops were left to secure the Baltic bridgehead, while 1,000 held Benfeld in Alsace for political reasons, as the only Swedish outpost in the province coveted by France. Others were spread across the remaining bases, while 7,500 field troops were positioned in Franconia and Thuringia, with Wittenberg and another 5,700 in Silesia and Moravia. Other detachments left only 12,500 cavalry and 6,000 infantry in the main strike force under Wrangel, with an additional 1,500 cavalry under Königsmarck as the advance guard. The Hessians, still numbering around 10,000, were fully occupied holding their existing positions. This greatly increased the significance of Turenne’s return to the Upper Rhine at the end of 1647 with 4,000 horse and 5,000 foot. A further 8,000 French held Breisach and other posts in the Rhineland.
Melander’s hardest task for the emperor in 1648 was to prevent a conjunction of Turenne and Wrangel, since he mustered only 10,000 Imperialists and 14,000 Bavarians. Around half his army were cavalry, and there were other imperial and Bavarian detachments in south-west Germany and Bohemia. He ended the 1647 campaign between the upper Weser and the Main, between Wrangel on the lower Weser and Turenne on the Upper Rhine. His position was not only exposed, but also in a region already exhausted by the fighting in 1645–7. He could not move against either enemy without endangering his communications with Bohemia and Bavaria. It was more important politically to confront the Swedes, so Melander planned to draw them towards Bohemia while Lamboy and the Westphalian army advanced up the Rhine to threaten Turenne’s communications with France. Cologne autonomy helped frustrate this, because Elector Ferdinand refused to let Lamboy out of Westphalia. Instead, Lamboy continued his fruitless war against Geyso’s Hessian outposts for the rest of the year.
French possession of the middle Rhine gave them bridges nearer the Swedish position. Turenne crossed at Mainz with 6,000 men on 15 February and marched east up the north bank of the Main while Wrangel moved south up the Weser to join him. Melander escaped their clutches by retreating south east to Nuremberg. The allied onward march was temporarily blocked by snow and disagreement between their commanders. Eventually they advanced south over the Main into Franconia, picking off minor garrisons. Melander retired slowly, while Gronsfeld positioned the Bavarians at Ingolstadt. The allies captured Donauwörth together, but then parted; the arguments over the Swedes’ incorporation of Turenne’s mutinous cavalry into their army the year before masked deeper political disagreements about the direction of the war. Mazarin was still reluctant to fight Bavaria and Turenne withdrew north-west to the Tauber valley to benefit from the spring grass and recuperate while the dispute was resolved.
Wrangel meanwhile marched north-east to capture imperial posts in the Upper Palatinate and relieve Eger, which had been blockaded since the autumn. His shift of focus was in line with Sweden’s overall strategy of delivering a substantial blow to the Habsburg hereditary lands to force Ferdinand to make peace. However, Swedish generals also saw a renewed attack on Bohemia as their last chance to plunder that country before the inevitable peace. As Wrangel was unable to break through from Eger, he won Turenne’s agreement to further joint operations intended to knock out Bavaria and invade Austria along the Danube instead.
The Battle of Zusmarshausen
Melander was too weak to exploit his enemies’ brief estrangement, and had received secret instructions not to risk the army. Ferdinand recognized that a victory would now bring only modest benefits at the congress, whereas a defeat could be catastrophic. Melander moved westwards to between Ulm and Augsburg to ease the supply situation and was joined reluctantly by Gronsfeld and the Bavarians. Their combined effective strength had dropped to 15,370 and around 2,000 of the 7,220 cavalry were now without horses.
The allies marched south-west to Württemberg, before swinging back east to Lauingen, a French-held outpost on the Danube downstream from Ulm. They crossed on 16 May and headed south to cut Melander off from Bavaria. Already aware of their approach, Melander had withdrawn eastwards through Burgau to Zusmarshausen. Nonetheless, news that the enemy was actually across the Danube caused alarm when it reached him that evening. He rejected Gronsfeld’s advice to march north to confront them, because it was unclear how many were already over the river. Instead, he continued eastwards heading for Augsburg to escape over the Lech into Bavaria. The decision placed him in a position similar to Mansfeld’s at Mingolsheim or Duke Christian’s at Höchst and Stadtlohn of having to retreat encumbered with baggage in the face of the enemy. He had to cover a 20km stretch through wooded hills between the Zusam and Schmutter streams to reach the Lech valley. Raimondo Montecuccoli was left with 800 musketeers and 2,000 cavalry and Croats as a rearguard, while Melander set out with the rest of the army at 4 a.m. on 17 May.
Wrangel and Turenne had a considerable numerical superiority at 14,500 cavalry and 7,500 infantry, but were hindered by the terrain from deploying this to full effect. The action developed as a running battle with Montecuccoli’s rearguard as it fell back along the narrow route through the forest. The allied vanguard of three French and six Swedish cavalry regiments attacked around 7 a.m. Montecuccoli held for more than an hour, before retiring over the Zusam stream once it became clear the entire enemy army was arriving. He fell back to where the forest narrowed at Herpfenried village, intending to resist until Melander could establish another position further on at Horgau. The French cavalry worked their way along the easier southern side of the road and outflanked Montecuccoli. Melander dashed back with his bodyguard to rescue him. The rush to get going that morning had left Melander no time to put his armour on and he was hit in the chest by a pistol shot and killed shortly before midday. Imperial detachments continued to resist, but the fighting became confused as the French and Swedes pushed up the road, capturing part of the baggage.
Montecuccoli’s resistance nonetheless bought time for Gronsfeld to get the bulk of the army across the Schmutter just east of Biburg and to dig in on the Sand Hill on the other side. The Bavarian entrenchments had already reached knee height by the time Montecuccoli crossed with the survivors of the rearguard at 2 p.m. Bavarian pioneers then destroyed the bridge before the allies could appear in strength. The French used six captured cannon to support an attempted crossing, but were beaten back. Their infantry were still toiling along the road, denying them the advantage of numbers. Gronsfeld was able to slip away at night to Augsburg, having lost 1,582 casualties, but only 315 prisoners and 353 wagons. Melander’s objective had been achieved, but it could have been done with less cost had the baggage been sacrificed.
The allies had failed to destroy the emperor’s last army and it continued to repulse probes along the Lech. Gronsfeld had learned from Tilly’s experience in 1632 and remained well back from the river, ready to pounce as the enemy crossed. Wrangel wanted to win fame by repeating Gustavus’s feat and began sending cavalry swimming across on 26 May. One of Gronsfeld’s patrols encountered them and mistakenly reported that the entire enemy army was already across. Gronsfeld retreated to Ingolstadt, exposing southern Bavaria to the enemy as in 1632–3 and 1646. The main imperial army dissolved in the retreat, falling to only 5,000 effectives, with the Bavarians numbering not many more. Gronsfeld had been shaken by Zusmarshausen and the constant alarms of the previous two weeks. This final retreat cost him Maximilian’s confidence and he was arrested along with two subordinates on 3 June and replaced by General Hunoldstein, who was followed in turn by Enkevort in August.
The elector vented his frustration on the army, and commandants of minor positions like Windsheim found themselves executed if they surrendered. More realistically, the crisis prompted him to drop his objections to Werth who was ordered to collect 6,000 imperial cavalry from Bohemia to reinforce the Bavarians. Ferdinand meanwhile entrusted imperial command to Piccolomini who had been without a position since resigning in the Netherlands in 1647. They were all competent officers, but it would take time to reorganize the demoralized army behind the river Isar. In the meantime, Maximilian joined 12,000 of his subjects and fled to Salzburg, where he had already placed his archive and treasury for safe keeping two years before.