The complete set in detail

RA40
Sc.No. C40
1931 - Air, commemoration of the 'Graf Zeppelin' trip : Brown overprint 'Polarfahrt' - red ; 1 Mk.

RA41
Sc.No. C41
1931 - Air, commemoration of the 'Graf Zeppelin' trip : Brown overprint 'Polarfahrt' - ultramarine ; 2 Mk.

RA42
Sc.No. C42
1931 - Air, commemoration of the 'Graf Zeppelin' trip : Brown overprint 'Polarfahrt' - sepia ; 4 Mk.