I received a rare one in the mail today, so here's another little bit of philatelic history.
On 11 April 1914, the Rudolf Hertzog mail-order house of Berlin arranged for pilot Bruno Buchner to take a Pfalz biplane to German Southwest Africa (DSWA) for an exhibition to be held in Windhoek, DSWA, on 29 May-4 June 1914.Buchner's Pfalz Biplane in DSWA
The aircraft was assembled in Swakopmund, DSWA, and made several trial flights on 14 May 1914. At some point, the decision was made to have the plane conduct several airmail flights on 18 May 1914. The aircraft was to fly along the railway line from Swakopmund-Usakos-Karibib-Okahandja-Windhoek, landing at each town and carrying mail.
The flight started in Swakopmund on 18 May 1914 at 0630. The mail picked-up in Swakopmund was stamped with a single-line, violet rubber stamp "Erster Flugpostversuch in DSWA" (First airmail attempt in DSWA). Mail with this cachet catalogs in Friedemann as Fr. FN1.Fr. FN1
After an emergency landing en route, Buchner arrived in Usakos (83 miles/133 km away) in the late afternoon of 18 May 1914. The following morning (19 May 1914), he departed for Karibib (17 miles/27 km away) at 0700, arriving there 20 minutes later.
Mail posted in Usakos received a 3-line rubber stamp "Luftpost Usakos-Karibib / 1 Flugzeug in Südwest / befördert" (Usakos-Karibib airmail / 1st airplane in Southwest / transported). Mail with this cachet catalogs in Friedemann as Fr. FN2.Fr. FN2
Due to the weather, the flight couldn't proceed from Karibib as scheduled on 19 May 1914. Instead, local exhibition flights were conducted on 20-21 May 1914. On 22 May 1914, the airmail flights resumed with the flight from Karibib to Okahandja (69 miles/109 km). Because of the delay, mail for this leg typically carries one of two cancel dates - 19 May 1914 (mail accepted for the originally scheduled flight) or 21 May 1914 (mail accepted during the delay). The mail accepted in Karibib bears a 3-line cachet - "Erste FLUGPOST / Swakopmund Karibib Windhuk / Deutschsüdwestafrika" (First airmail / Swakopmund Karibib Windhuk / German Southwest Africa). The cachet is typically in green ink for the 19 May 1914 mail, and in black-violet ink for the 21 May 1914 mail. Mail with this cachet catalogs in Friedemann as Fr. FN3.Postal Stationery MiNr. P19 I, use catalogs as Fr. FN3 - click to enlarge
On 24 May 1914, Buchner left Okahandja for Windhuk (42 miles/67 km away), but he had to make emergency landings in Teufelsbach and Brakwater due to bad weather en route. He finally landed on the Windhoek racecourse on 27 May 1914. Mail carried from Okahandja received a 3-line violet cachet - "Erste FLUGPOST / Deutsch Südwestafrika / Okahandja Windhuk" (First airmail / German Southwest Africa / Okahandja Windhoek). Mail with this cachet catalogs in Friedemann as Fr. FN4.Fr. FN4
These were the only airmail flights ever conducted in German Southwest Africa. Mail carried on these flights is exceptionally rare, and I was lucky to get the copy of FN3 above for a "reasonable" price.