He saw only limited involvement in the Battle of France in 1940, but his units played a decisive role during the German invasion of Greece in 1941 and, later the same year, during the Siege of Sevastopol and other operations in the Crimea.

[3][2] His father was director of a sugar factory in Ober Pritschen in Silesia, estate owner and a retired captain of the Prussian Army.

[4][5] After completing his high–school studies, Franz Mattenklott applied to enter an infantry regiment in Metz, Alsace-Lorraine, then part of the German Empire.

The following years, disregarding the confining Versailles Treaty, the Nazi regime intensified the German re-armament (Aufrüstung) and increased the size of the military.

As part of this process, Mattenklott received the command of the newly formed Infantry Regiment Stargard on 1 October 1934 and he was promoted to Oberst (Colonel) on the same day.

Gebirgskorps) of General der Infanterie Franz Böhme, part of Generalfeldmarschall (Field Marshal) Wilhelm List's 12th Army (Wehrmacht).

[14] The invasion began on 6 April, and until the night, Mattenklott's troops had failed to punch through the Metaxas Line, suffering heavy casualties.

[15] Most of the Greek forts continued to resist until 9 April, but as the main forces were isolated by the German advance to the west, they finally capitulated on the same day.

When 400 Jewish men and 10 women were shot, ostensibly for acts of sabotage, Mattenklott "expressed his recognition and gratitude" to the responsible Einsatzgruppe D for the executions.

[21] Mattenklott's units, along with XXX Army Corps, spent the next months in bitter fighting over eastern Crimea, managing to repulse Soviet attacks, suffering and inflicting heavy casualties.

[24] Almost immediately, he became confronted with the problem of the nutrition of the population, as the callous policy of Manstein was to confiscate all raw materials to sustain the German troops.

[26] Under Mattenklott's command, hundreds of civilians were executed, including those accused, often wrongfully, as partisans, communists, invalids and the homeless, as well as numerous other groups labeled as "undesirable elements" by the Nazi world view.

[2] Mattenklott commanded the XLII corps during the battle of Kursk in July 1943, but his unit played only a marginal role in the Wehrmacht's last major offensive against the Red Army.

During the ensuing battles, the head of the anti-Nazi National Committee for a Free Germany, General der Artillerie Walther von Seydlitz-Kurzbach, unaware of his absence, appealed with letter to Matteklott and other commanders, urging them to surrender so he could halt the impending destruction.

[31] After weeks of hard fighting, the Germans achieved a breakout, and Mattenklott was summoned back to oversee the refitting of the corps and the transfer of the units in occupied Poland, away from the frontline.

Exactly one week later, on 22 June 1944, the Soviet launched a large-scale offensive, Operation Bagration, which shattered the Wehrmacht units and paved the way for the drive into Germany.

Unbeknownst to Mattenklott, who apparently did not harbour any kind of anti-Nazi sentiments, some of his officers in the Wehrkreis VI were involved in the military resistance against Hitler.

Soon thereafter, the commands from the conspirators' center in Berlin for the immediate arrest of the members of the Nazi apparatus in the Wehrkreis were signed from the retired Field Marshal (Generalfeldmarschall) Erwin von Witzleben.

[33] To what extent the failure of the plot and the brutal response against those involved in it affected Mattenklott's stance towards the evergrowing denialism showed by Hitler in view of Germany's impending defeat is not known.

During his interrogation on 19 May 1947, Mattenklott claimed that such measures were "necessary and justified", but explained that he considered them to be of deterrent nature, as he stated that an execution of an armed civilian never came to his attention.

He also told his interrogators that he had no knowledge of the systematic killing of Jews, Communists and other "undesirable elements" in the East, and categorically denied any involvement.

[36] Only in the decades that followed did it became known that Mattenklott was fully aware of the Nazi policy of destruction and genocide in the Soviet Union, the activities of the Einsatzgruppen and that he often praised the "excellent cooperation" his units had with the perpetrators of these crimes.

One of them, the Generalmajor a. D. (retired) Paul Goerbig, president of the court-martial that convicted Gräfer, was arrested in Hamburg in April 1949 and brought to Paderborn.