In 1929 Guderian encountered real tanks for the first time. On a trip to Sweden he was given hospitality by a Swedish tank battalion which permitted him to learn to drive one of their M21 tanks. Having gained some 'hands on' experience must have boosted his confidence about tank operations. In 1930 he took command of the 3rd Prussian Motor Transport Battalion, which was equipped with some real armored cars, dummy tanks and anti-tank guns. One area in which Guderian's influence proved to be of considerable importance was communications; the key to command and control. By the outbreak of the war every German tank had at least a radio receiver and every command tank had a transmitter, which gave the German armored formations an extremely high degree of tactical flexibility. 

Many senior officers, often artillerymen, were not prepared to accept Guderian's ideas without the necessary proof, and reminded him that he was not a Kriegsakademie man; he was a technician with inadequate understanding of the higher strategic thought process. However, one of the panzer arm's most enthusiastic proponent was none other than Adolf Hitler, Germany's new Chancellor, who had exclaimed, on witnessing one of Guderian's demonstrations involving a motor-cycle platoon, two armored car platoons, a platoon of experimental PzKpfw Is and an anti-tank platoon: 'That is what I need! That is what I'm going to have!' 
 
 

After the invasion of the Sudetenland Guderian became Chef der Schnellen Truppen, being responsible for recruiting, training, tactics and technique of all the Wehrmacht's motorized and armored units. In 1938 he published his highly influential book on armored warfare, Achtung-Panzer!. The book explained his logic ideas on how German armored units should be built up. One thing Guderian was worried about was the raising of tank brigades for close co-operation with infantry divisions, as employment of tanks merely in support of unmechanized infantry was a reversion to the practice of 1916-18. Tanks in this role might have some limited tactical utility but could have no operational impact. One of his conclusions was that the greatest results could be achieved when massed tanks are used with the benefit of surprise.

He had by then been promoted to General der Panzertruppen and on the outbreak of war was given commend of the Nineteenth Corps, which he led in the Polish Campaign. For the battle of France he was given a Panzer group, and his brilliant handling was a perfect demonstration of the concept of blitzkrieg -rapid armored breakthrough, supported by air power, on a narrow front- which he had propagated in his writings. Every German tank had a wireless communication system and were set in action as whole and independent units and were not attached to the Infantry units, with Guderian driving relentlessly as far as his men and tanks could go, wrecking havoc far beyond the expected front-line. It were his tanks which were first across the Meusse, at Sedan (14 May 1940), and first to reach the Channel coast (20 May). Guderian always believed in being at the front so that he could take personal control whenever necessary. 

Guderian played a decisive part in the victory over France in 1940, although he was forced by an overcautious High Command into making unnecessary stops. First at the bridgehead at Sedan on 15 May, again at the river Oise on 17 May (the next day he was permitted to do "reconnaissance in strength" only towards the coast), and finally just outside Dunkirk on 24 May. Although Dunkirk was the Allies' last possible exit for evacuation of French and English troops from Belgium, Hitler suddenly ordered a halt to Guderians panzers, allowing the Allies to evacuate the British Expeditionary Force back to England from 28 May until 4 June. 

Top: As Inspekteur (inspector-general) of the Panzer troops, Guderian always wanted to understand everything in detail. Here he listens to the experiences gained with the new Tiger tank. 

Right: Guderian meets two officers captured in France. His panzers succeeded to win the battle of France, something the complete German Army had not been able to achieve after four years fighting during the First World War.

The final drive on Moscow continued in October under the code-name Typhoon, when suddenly the winter rains set in, resulting in Guderian's panzer stuck in the mud, and making supply of ammunition, fuel and food almost impossible. By 14 November Guderian's panzer group, having crossed the frontier in June with 600 tanks, possessed only 50 operational machines. Rain was followed by winter, the worst in living memory, with blizzards from innermost asia end deep cold.When Guderian was finally halted by a combination of the Russian winter, exhaustion and enemy's counter-attacks, he had reached Moscow's suburbs, but was unable to hold his ground. 

Hitler turned his wrath against Guderian and other professionals, the very men who for two years had won him outstanding victories, and dismissed many commanders, including Rundstedt, Leeb and Guderian. Shaken by the Stalingrad debacle and the events in Africa, Hitler recalled Guderian to duty on 1 March 1943 as Generalinspekteur der Panzertruppen, again responsible for modernizing of the armored troops. Responsibilities included the equipment, organization and the training of the Panzerwaffe in the broadest possible sense. This brought not only the Army's panzer and panzergrenadier divisions within his orbit but also the armored troops of the Waffen SS, the Luftwaffe and even the armored trains. The only exception was the Assault Artillery, since at the tactical level the assault Artillery performed their tasks so efficiently as not to justify outside interference. 
 

After the traumatic experiences of the past year, Guderian had the task of setting the Panzerwaffe as a whole back on its feet. He advised Hitler that the Panther was not ready before August 1943, so the up-gunned PzKpfw IV remained the mainstay of the tank battalions, and required the new type of equipment, including second generation tank-destroyers to replace the Marder and half-tracks for the panzergrenadiers. Guderian also designed humorous booklets to replace the usual stodgy manuals for tank crews, which were written in everyday soldier's slang and covered every aspect of maintenance and life aboard a tank, cartoons and multiple 'do's and don'ts' for each crew member. He retained the post, through constantly at odds with Hitler, until 21 March 1945, when he was finally dismissed. Although he was interrogated about war crimes no serious evidence was found against him and he was released without being indicted.