The fact this claim has been at the top of this Hacker News thread for hours piqued my interest. So I did some research.
I read the New York Times "Overlooked" obituary for Dr Liang Sicheng but found no reference to this event. [1]. The closest thing I could find was [2] which writes the following (and links to a currently-unavailable article hosted on the government of China mouthpiece China Daily):
> During World War II, as Japan occupied Beijing and most of coastal China, Liang Sicheng was working in Sichuan. According to Luo Zhewen, a former student who frequently assisted Liang Sicheng in his research, Liang heard that the Allied forces were planning on bombing Japan and Japanese-controlled areas in China. Liang began drawing up a map of the major Chinese cities occupied by Japan as well as Japan’s former capitals, Nara and Kyoto to help American military planners avoid destroying important historic sites and buildings. Liang then traveled to Chongqing, the wartime capital of the Republic of China, and passed the maps to the US Army liaison stationed there.
The NYT article suggests Dr. Liang Sicheng was later in life sent to re-education as a counterrevolutionary of Maoist China, but that he has had his reputation revived by the CCP which turn him into a folk hero. I don't doubt that he passed on maps and messages to the US Army in the hope of sparing culturally important sites from bombing, but without further evidence the claim that he was an advisor to the US military that convinced them to spare Kyoto and Nara appears overblown.
I am happy to be convinced if independent historians believe Liang Sicheng had a part to play in the decision, but right now this claim feels like highly-upvoted CCP propaganda.
[1] https://www.nytimes.com/2018/04/11/obituaries/overlooked-lin...
[2] https://radiichina.com/did-chinese-architect-liang-sicheng-s...