Hermann Oberth writes to Goddard for a copy of his 1920 monograph, 'A Method of Reaching Extreme Altitudes'. Goddard, concerned with German interest in space flight, sends him a courtesy copy with some apprehension. The following year Oberth reciprocates by sending Goddard a copy of 'Die Rakete zur Weltraumfahrt', including an acknowledgement of Goddard's work in an Addendum ('...Goddard's work was received just as this was going to press....my theoretical approach is supplemented by his practical work....'). Goddard is convinced that Oberth has borrowed his ideas and refers to him as '..that German Oberth...'.