During the period of his retirement which came in 1911, he began to study the farm lands of East Prussia socketed with the lakes and swamps. This was to be the battleground of an inevitable war with Russia. He began to study the region until he knew every square mile by heart from Königsberg on the Baltic down through the network of lakes south of Tannenberg. On paper he fought there a thousand different campaigns. It is said that he became almost fanatical on the subject. In his classes at the War Academy where he was an instructor he became known as The Old Man of the Swamps. He used to go round Berlin with a folder of maps, and any officer whom he could buttonhole, he drew him aside and talked of the Masurian lakes. He became so obsessed with this subject that officers fled at his approach. They began to call him Swampy Hindenburg. But as he rose in rank and as he commanded troops during the maneuvers in East Prussia, the General Staff realized that Hindenburg knew the country.
There came a day when Von Hindenburg was appointed umpire of a big maneuver in East Prussia. The Army of the Red--so the story runs--was commanded by the German Emperor, opposing him was the Army of the Blue. The sham battle ended rather undecisively. The Emperor and all the lesser generals met in the center of the field at the Grosse Kritic to hear the criticisms of umpire Von Hindenburg. Hindenburg was unmerciful. He tore the reputation of the General of the Blues to tatters. He demonstrated that this officer had made the grossest blunders. For half an hour in unsparing language Hindenburg, who had his own ideas about how every battle in East Prussia should be fought, criticized the General. It occurred to the Emperor that Von Hindenburg was concentrating his criticism upon the Army of the Blue and that he had said nothing whatever about the Army of the Red, which the Kaiser himself commanded. The Kaiser asked Von Hindenburg about this, remarking that it was noticeable that nothing had been said about his army and adding that for the benefit of all the officers the Army of the Red should also be criticized. Von Hindenburg continued to say nothing about it. Again the Emperor asked him.