When the Nazi Party took power in Germany at the beginning of 1933 his problems greatly intensified: he had already been dismissed from one teaching post, and participated in (now illegal) resistance to the government.
After he helped a Soviet officer to escape by returning the man's gun he found himself before a military court which conferred a double death sentence on him.
The port facilities at Hamburg were booming during the early years of the twentieth century, and by the time Rudolf Klug was born in 1905 his father was working not as a butcher but as a dock worker.
In 1916 his younger brother, Ernst-Otto was born, and with the household budget under pressure Rudolf took work as a part-time errand boy, although his mother had to be persuaded to lie about his age for this to be possible.
He qualified in 1927 (which was also the year in which his father died following a work accident at the docks) and took a teaching post at the Secondary School in Hamburg's Telemann Street.
While he was considering the need to broaden the access of working class children to education he became a co-founder of the so-called "Proletarische Volksheim-Jugend" organisation.
[1] Hamburg city politics during the later 1920s reflected national trends, with the Social Democrats and traditional conservative parties losing out to the Communists on the left and, even more starkly, to the Nazis at the other extreme.
Rudolf Klug became involved with the "Interests Community of Opposition Teachers" ("Interessengemeinschaft Oppositioneller Lehrer" / IOL) which was created in 1931 in order to "oppose the dismantling of social rights and achievements in education and the growing risk of fascism".
[n 1] As a popular young teacher who was also a Communist Party activist Rudolf Klug generated mistrust at an increasingly jittery city hall, both among the Nazis and among the traditional conservatives.
Klug's name appeared in an advertisement in several Hamburg which listed a number of teachers "on leave from the schools service" (""aus dem Schuldienst beurlaubt"").
He was imprisoned at Wolfenbüttel till 11 August 1934, after which he was involved in forced labour at a young persons' holiday camp on the Island of Sylt.
[1] By the end of 1934 he was back in Hamburg and had taken work with the little coffee trading business set up near the dockside by the former municipal politician Kurt Adams.
Two things he had in common with Adams (and with his fellow employees) were that he needed to support himself financially and that he had been deprived of his chosen career for reasons of politics and / or race.
Later he found work as a credit control book keeper in Hamburg's Lurup quarter with an abrasives producer called Christiansen & Co.
According to his sister he was persuaded by comrades in the Bästlein-Jacob-Abshagen Group to apply to have his "fitness for military service" restored in order that he might join the army and create political opposition to the Nazis inside it.