Junkers A 32

The Junkers A 32 was a mail plane built in prototype form in Germany in the late 1920s, and later developed as a prototype reconnaissance-bomber under the designation K 39. The design was a conventional low-wing cantilever monoplane with fixed tailskid undercarriage. Construction was metal throughout, with corrugated duralumin skin. Three open cockpits were provided in tandem; the third seat intended from the outset to accommodate a tail gunner for a military version of the aircraft. In fact, the militarised version developed in Sweden by AB Flygindustri featured a fourth crew position as well, for a bombardier. This version featured twin machine guns built into the engine cowling, and a trainable machine gun for the tail gunner. Only two A 32s were built, and the first prototype was destroyed in a crash on 2 November 1927 that killed Junkers engineer Karl Plauth. The sole K 39 constructed may have been modified from the second prototype. No sales of either the civil or military version ensued.

Summary from Wikipedia, photo via Wikimedia Commons, licensed under CC BY-SA.