In all these Turenne took much more than his full share, paying attention not only to his own duties but to all that was being done, spending his whole time in the batteries and the trenches, and in learning all that was possible of war carried on under such conditions.  In the winter, operations were always suspended, and Turenne spent his time in Paris, where his manner and conduct won for him the favour of all with who he came in contact.  He had been severely brought up under a Calvinist tutor; his habits were simple, his tastes quiet and almost ascetic, and he cared little for the amusements of the brilliant and corrupt court.  When the war with Lorraine broke out, Turenne at once sought for employment with the French army.

He recognized that there was comparatively little to be done in the war of sieges in Holland, and longed to enter a wider field.  His request was gladly granted, for the presence of the Duc de Bouillon’s brother in the French army was in itself some guarantee of the duke’s fidelity to his engagements with France, and Turenne was at once appointed to the colonelcy of a regiment.  He devoted himself as assiduously to his work as he had done in Holland, and it was not long before his regiment gained the reputation of being the best disciplined in the king’s service.  He took part in a short expedition in 1630, but there was on that occasion no fighting, and he first saw real service under Marshal de la Force in 1634.  After the siege of La Motte, the success of which was due to the storming of the breach by Turenne and his regiment, and for which exploit he was promoted to the rank of Marechal de Camp, a rank equivalent to that of major general, he took part in several sieges, until Lorraine was completely conquered and its duke driven to abdicate and retire to Austria.

The battle of Nordlingen showed Richelieu that if France did not resolutely enter into the conflict the Austrians would become absolute masters of all Germany.  He at once signed a treaty with the Swedes, agreeing to grant them large subsidies to carry on the war.  By a similar treaty he promised subsidies and the province of Alsace to the Duke of Saxe-Weimar.  He entered into an arrangement with the Dutch, who were to aid France to conquer Flanders, which was to be divided between the two powers; while the Dukes of Savoy, Parma, and Mantua agreed to undertake, in alliance with France, the invasion of Milan, and to receive in return a portion of the territory won from Spain.  At the same time France declared war against Spain.  It was to the army commanded by Cardinal de la Valette, which was to act with that of Saxe-Weimar against the Imperialists, that Turenne was attached.