Antoine de Marbot recounted an incident that demonstrated the properties of the two styles of cuirass, when at Eckmühl in April 1809 French and Austrian cuirassiers crashed together, while the accompanying light cavalry drew off to the flanks to avoid being caught up in the fight.
The cuirassiers advanced rapidly upon each other, and became one immense melée. Courage, tenacity and strength were well matched, but the defensive arms were unequal, for the Austrian cuirasses only covered them in front, and gave no protection to the back in a crowd. In this way, the French troopers who, having double cuirasses and no fear of being wounded from behind had only to think of thrusting, were able to give point to the enemy’s backs, and slew a great many of them with small loss to themselves. [When the Austrians wheeled about to withdraw] the fight became a butchery, as our cuirassiers pursued the enemy. This fight settled a question which had long been debated, as to the necessity of double cuirasses, for the proportion of Austrians wounded and killed amounted respectively to eight and thirteen for one Frenchman.
A further item of protective equipment used by heavy cavalry was a consequence of the knee-to-knee charge formation: the long boots worn to prevent the legs being crushed. Some thought them more an encumbrance than a protection, as Marbot observed of a dismounted cuirassier officer at Eckmühl who was unable to run fast enough to escape the enemy – he was killed in the act of pulling off his boots
At Landshut one of the Archduke’s Corps (V) attacked a strong force of Bavarians, driving it from the town, before turning to attack an isolated French force under Davout occupying Regensburg. Unfortunately, the Archduke had discovered too late that Davout was unsupported. While Archduke Charles pulled back, having failed to destroy Marshal Louis Davout’s III Corps during the action at Teugn-Hausen on 19 April, Napoleon launched his counteroffensive on the following day, splitting the Austrian army in two. Napoleon pursued what he erroneously believed was the main force southward toward Landshut, leaving Davout and Marshal François Lefebvre to deal with what he perceived as an Austrian rear guard. However, on 21 April, as Davout closed in on the village of Eckmühl, he realized that he faced a much stronger force. Despite this Davout attacked, but a tenacious Austrian defense held firm.
Archduke Charles could have been crushed 24 hours earlier, but Napoleon had now arrived. With his arrival, the uncoordinated and disparate French forces began to take on some cohesion. But even Napoleon misread what was happening. He did not realise until it was almost too late that Davout was facing most of the Archduke’s army.
Davout sent Napoleon a number of messages during the day expressing his concerns, but it was only in the early hours of 22 April that Napoleon finally recognized his error.
As soon as he saw his mistake, his legendary skills of improvisation took hold immediately. Davout was supported by the bulk of Napoleon’s forces and a concerted effort was made to break the Austrian left, which was sheltering behind a battery of guns. Prince Rosenberg and his staff of IV Korps watched for two hours while 22 Austrian battalions held out against overwhelming numbers until 68 French battalions attacked them on three sides. As Napoleon committed his cavalry, Rosenberg’s retreat degenerated into a rout. Repeatedly he had asked Charles for reinforcements but repeatedly Charles had advised him to extricate himself as best he `thought fit’. The Archduke had no intention of sacrificing fresh troops on ground not of his own choosing.
Nevertheless, seeing panic taking hold among Rosenberg’s men, Charles immediately deployed a Cuirassier brigade and his Grenadier Reserve under Rohan to stem the tide. The Austrian cavalry slowed the French advance, forcing the infantry to form squares, but Rohan’s grenadiers with the exception of two battalions broke under the tide of IV Korps’s demoralised remnants. IV Korps was facing annihilation as a heavy mass of French cuirassiers approached to finish off its survivors.
It was 7 p. m. and the rising moon illuminated a dramatic scene. Six thousand French cuirassiers in two lines supported by their Württemberg and Bavarian auxiliaries advanced towards two much thinner lines of Austrian cuirassiers supported on their flanks by some squadrons of hussars. The tired French horsemen trotted forward while the Austrians with the gradient in their favour galloped towards them, about to break into a charge. As there were five French regiments against just two Austrian, this fight could only last a few moments and the Austrians were soon riding as fast as they could back to their lines. Two battalions of Austrian grenadiers appeared and formed square but were cut to pieces by St Sulpice’s Cuirassiers. The Archduke Charles himself escaped only with the greatest of difficulty. Exhaustion on the part of the French, and darkness, rescued the Austrians from annihilation. Charles however could take some consolation from the fact that he had husbanded his forces and he had not even committed 33,000 of his troops.
Thus ended the Battle of Eckmühl; unsatisfactory for Napoleon, who had not deployed his characteristic ruthlessness to inflict a `second Jena’ and highly unsatisfactory for the Archduke Charles, who had seen his elite units fail to rise to the occasion, though they had bought him the time necessary to effect an escape from the clutches of his foe.
In fact Charles’s position at this stage was stronger than it appeared. Eckmühl was a rearguard action fought by Rosenberg against a greatly superior enemy attacking him from the west, south and east. Two Austrian Korps, I and II, were far from demoralised and the Generalissimus still had his lines of communication with Vienna, though these now ran through Bohemia. True, II and IV Korps had been defeated and had retired in poor shape, but they had not been completely crushed. On the morning of 23 April Charles wrote to his brother, the Emperor, advising him to leave Schärding where he was awaiting results and not rely on the Archduke to be able to save either him or Vienna.
While Napoleon paused, Charles got most of his army across the Danube, leaving a small force to withstand the siege that was inevitable the following day when the French invested Regensburg. It was here that Napoleon received his only known wound in twenty years of making war, when a spent cannonball hit his foot. Napoleon’s failure to pursue Charles has been attributed by the renowned French military historian General H. Bonnal to his dwindling grasp of the strategic imperative to destroy his opponents. His Bavarian campaign involved his forces in three battles in as many days but each time Charles was able to withdraw in reasonable order. As the Austrians had lost two- thirds of their artillery the question rightly arises as to what might have happened had the French cavalry pursued them `epée dans les reins’. But Napoleon later admitted to Wimpfen that he never imagined the defeated Austrians would rise like a phoenix from the ashes within weeks.
Retreating across the Danube at Regensburg, the Austrian army marched through Bohemia to link up with the left wing of the army arriving from Landshut. The French advanced and occupied Vienna on 13 May. Eight days later the reunited Austrian army engaged Napoleon once more at the Battle of Aspern-Essling.