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[Ric Gillespie]

We're trying to decipher the meaning of the letters XRO on a document that might be related to the Earhart disappearance. The letters might stand alone or be part of a longer string of letters, but I can't think of an English word that includes the letters XRO together.  Any context is a possibility, but the document probably dates from not-earlier-than 1936 and not-later-than 1945.
Any ideas?

[Karen Hoy]

Does it refer to a Lockheed XRO-1 military aircraft?

historyofwar.org/articles/weapons_lockheed_XRO-1_altair.html

Karen Hoy ER 2610

[Don White]

What is the context, if you are at liberty to reveal it?

Karen's suggestion seems to fit in the context of long-distance flights. This from Wikipedia:

Altairs were used to carry out a number of record-breaking long-range flights. One aircraft, named Lady Southern Cross was used by Australian aviator Charles Kingsford Smith to carry out the first flight between Australia and the United States between October 20 and November 4, 1934. Kingsford Smith was killed in the early hours of November 8, 1935, flying Lady Southern Cross during an attempt on the record for flying between England and Australia.

Interestingly, the Japanese had two of them.

https://en.wikipedia.org/wiki/Lockheed_Altair

[Ric Gillespie]

Does it refer to a Lockheed XRO-1 military aircraft?

Good thought, but it wouldn't make sense in this case.  Lockheed also built a Model 10 for the Navy - XR2O-1  and one for the Coast Guard - XR3O-1.
The XR2O-1 is c/n 1052, now at the New England Air Museum restored as a Northwest Airways airliner.

[Ric Gillespie]

What is the context, if you are at liberty to reveal it?

Sorry, not at this time.

[Carshall C Carlisle III]

My first thought is an acronym such as X=Transmit, R=Receive, O=only which is probably something I just made up because I’m unable to find it in any aviation or military brevity codes.  The second thought was an airport or radio station Identifier before the K and W call signs began.  Seems the Dutch have a XRO airfield. I couldn’t find a radio station with those call letters.  My last thought was a teletype/telegraph code of sorts?.  I couldn’t find anything that jumps out other than in some telegraph code, XRO means "ram".  There was such things as cipher telegrams (FWIW) not knowing the context  of where these letters might appear.

[Carshall C Carlisle III]

An update to my earlier thread. 
XRO were the call letters for China's first radio station (1923 AM at 50 watts on 1500khz).

https://en.wikipedia.org/wiki/List_of_oldest_radio_stations

[Martin X. Moleski, SJ]

We're trying to decipher the meaning of the letters XRO on a document that might be related to the Earhart disappearance. The letters might stand alone or be part of a longer string of letters, but I can't think of an English word that includes the letters XRO together.  Any context is a possibility, but the document probably dates from not-earlier-than 1936 and not-later-than 1945.
Any ideas?

You might have to search for Xray Romeo Zero rather than Xray Romeo Oscar.

So, for example, XR0 (not XRO) is the code block for Easter Island.

Wes Lamboley, W8FMG "has been an active ham since 1954 and has operated from VK4, J28, KX6 and XR0."


XR0 can also mean "Exchange Rate 0": XR1 and XR0 are the exchange rates for current money in El Salvador against the US dollar from the first day of indexation and on the immediately preceding indexation date, respectively.

[Christophe Blondel]

My first thought is an acronym such as X=Transmit, R=Receive, O=only which is probably something I just made up because I’m unable to find it in any aviation or military brevity codes.  The second thought was an airport or radio station Identifier before the K and W call signs began.  Seems the Dutch have a XRO airfield. I couldn’t find a radio station with those call letters.  My last thought was a teletype/telegraph code of sorts?.  I couldn’t find anything that jumps out other than in some telegraph code, XRO means "ram".  There was such things as cipher telegrams (FWIW) not knowing the context  of where these letters might appear.

To concur with the first suggestion, here is a list of acronyms and abbreviations that identifies XRO as meaning "X-band receive only": https://onlinelibrary.wiley.com/doi/pdf/10.1002/0471728497.acron
Best regards
Christophe

[Christian Stock]

Transmit/Receive Only, on the same freq, as opposed to TO or RO?

[Bill Mangus]

I'll throw this idea out:

Could XRO or XR0 be a (partial) call sign for a ship -- civilian or military someplace in the pacific in July, 1937? 

[Christian Stock]

x-band receive only

Does this have to do with harmonics?

[Ric Gillespie]

Could XRO or XR0 be a (partial) call sign for a ship -- civilian or military someplace in the pacific in July, 1937?

Good thought.  I should be able to check that in the Berne List of ship and shore stations.

[Don White]

My first thought was that it would be an expression for something in radio or other technical context of the time.

I found a number of meanings for XRO that are too recent in origin: product names, pop culture references and computing ("exclude route object").

Found this too: https://ourairports.com/navaids/XRO/Florianopolis_VOR-DME_BR/

Don

[Randy Jacobson]

The possibility of a radio call sign jogged my memory, that perhaps it was an amateur station, often referred to as the final 3 digits (the first two being K5, K6, W5,W6 in the US).  I found a 1938 directory of amateur stations on the Internet, which is very useful.  The link is:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjW8v2Qo8vrAhVIu1kKHQupBvEQFjADegQIAxAB&url=http%3A%2F%2Fwww.hallikainen.org%2Forg%2Fkeh%2Fpdf%2FSpring_1938_Radio_Amateur_Callbook_District_6.pdf&usg=AOvVaw0lTK1W_M4wJZ7S24bN2PeO

What is shows is that for at least the US in that time period, no amateur station had an X as the third digit.
At least we can rule that line of investigation out.