There is a curious idea floating around, that World War One commenced on the 9th day of the month of Av. (For example, here, and here, and here.)

I call it curious, since it takes a fairly creative reading of history to see the war as having begun on a single date in particular, and specifically on the 1st of August, 1914. Already on the 28th of July, Austria had declared war on Serbia, and the first shots of the war were fired on the 29th. Those two dates correspond to the 5th and the 6th of Av, respectively. It was on the 9th of Av (already after Russia had fully mobilised) that Germany invaded Luxembourg and declared war on Russia, but I am not aware of there being a single historian who thinks that was "the beginning" of the war. (For more information on these events, see here).

I would like to know, when did people first start suggesting that the war began on the 9th of Av? Was it during the war (1914-1918) itself? Was it during the interwar period? Or was it specifically during or after the Holocaust?

Note: There is a long tradition of relating the 9th of Av to specific tragedies that have occurred to the Jewish people - a tradition that has its origins in the Mishna, Taanit 4:6. I'm not querying why people would want to fit the first world war into this model, but only when people first started doing so.