Over at The Appendix, 'a new journal of narrative & experimental history' to which you can subscribe, Felipe Fernandes Cruz has reproduced some intriguing declassified US documents from the early 1940s concerning rumours of clandestine German airfields in Brazil. The reason for the US interest in any evidence of German activity in South America, apart from the Monroe thing, seems to have been the possibility of an air raid on the Panama Canal. It's not clear how the three documents relate to each other, as they're from different agencies (FBI, US Army) and dates (October and December 1941, July 1942) and don't appear to directly refer to each other. It seems that they reflect an ongoing concern about the possibility of German aerial activity in the Amazon rather than a response to any particularly credible information.
The first document, dated 3 October 1941, is simply J. Edgar Hoover informing the Assistant Secretary of State, Adolf A. Berle, of 'rumors current in Brazil as to a secret German air base, reported to exist in the Rio Negro district of the upper Amazon' and promising to forward any further information as it was received. The second chronologically is dated 18 December 1941 and appears to be an intelligence summary for the US Army Chief of Staff (George C. Marshall) from the Assistant Chief of Staff. It's actually a bit sceptical of the idea, saying 'It is our opinion that the danger from secret landing fields in this region is much less than has formerly been rumored', due to the difficulty in shipping the large quantities of fuel required up the Amazon. However, it also identifies a group of Germans already established in Amazonia who could have been gathering supplies for years:
In this region at the present time is a large group of German monks and their abbeys. They have been firmly established in this region for the past 80 years, and know this region possibly better than any Brazilian. There is a possibility that for some time past air supplies may have been secretly built up at points in this region which might be used for attacks on the Canal. It is to be remembered that this is a vast region, the single State of Amazonas being two and one-half times larger than the State of Texas.
The final document appears to be a report to the War Department from someone named Abbott in Manaos, and is dated 8 July 1942. This is the one that interests me the most:
Reliable reports huge quantity gasoline unknown quality in transit up Beni River in May believed destined Germans Riberalta Bolivia. Small bits unverified information many separate sources indicates possible Axis planeed [sic] series ground facilities for long range planes reach Venezuela: one from Beni River with one halt enroute. Two from Mato Grosso Area with probably two halts. SUch [sic] program logical for approach to Panama but no reports unknow [sic] planes such localities. Major Harlow taking both planes Belem ninth for minor repairs. Plan flight up Rio Negro next week using fuel sent from here. No instructions received except cables.
These rumours about secret German airfields in the Amazon in 1942 are clear analogues to the rumours about secret German airfields in Australia in 1918. So why were there 'no reports [unknown] planes', as there certainly were in Australia? This looks like it could be another useful test case.
It's possible that Brazilians, even in the remote Amazon, were by 1942 reasonably familiar with aircraft and so less likely to mistake non-aircraft for real ones, or to be surprised by real but non-German ones. Mystery aircraft scares were increasingly scarce by this time around the world, for I think just this reason, and were only reinvigorated by the imminence of new jet and rocket technology. I don't know enough (or anything) about aviation in Brazil at this time to say whether this is the case, but there is evidence even in these documents that aircraft were already an essential tool for mobility in what was very inhospitable terrain.
But there's also the question of the source of these rumours: they may not be such a clear analogue to the earlier Australian episode after all. Just who was passing these stories of secret German airfields around? Was it ordinary Brazilians? Brazilian military personnel? Expatriate American or German residents? It makes a difference, because such stories would mean different things, and would be used for a different purpose, by different audiences. Did Brazilians themselves fear German infiltration? I doubt they were as worried about a German air raid on the Panama Canal as the Americans were. I need to know more!