The claim that George H. Kerr was spying for the U.S. during his first period in Taiwan (1937-1940) has resurfaced, this time in a 2017 publication by respected historian Chen Tsui-lien (陳翠蓮), 《重構二二八：戰後美中體制、中國統治模式與臺灣》 (Reconstructing 228: The Postwar US-China System, China's Ruling Model, and Taiwan**).
Chen cites three sources that claim Kerr collected intelligence for the US during his time as a teacher in Japanese-controlled Taiwan. The first, Huang Jinan (or N̂g Kí-lâm [黃紀男]), wrote that Kerr was sent to Taiwan by the Central Intelligence Agency as a spy (臥低的間諜). Chen neglects to point out the problem with N̂g's story: there was no CIA before 1947--even its precursor, the Office of Strategic Services (OSS) wasn't established until 1942 (the OSS's precursor, the Office of the Coordinator of Information, was established in 1941).
The second source, Wu Hongren's (吳宏仁) 一個家族。三個時代:吳拜和子女們 (which I am still reading after all these months!), says that after WWII, when someone asked Kerr about why US bombers avoided bombing Taipei First High School (台北高校), he admitted that he had been on a mission to collect intelligence about Taiwan during his time teaching there in 1937-40. However, the "someone" (有人) of whom Wu speaks isn't clear (in fact, it could very well be N̂g--Wu doesn't specify that it was a former student).
The third source that Chen uses is an indirect quote from Wang Chengxiang's (王呈祥)'s awful book, 《美國駐台北副領事葛超智與｢二二八事件｣》 (U.S. Vice-Consul in Taiwan George H. Kerr and the "228 Incident"). Wang at least points out that Kerr couldn't have been working for the CIA at that time, though somehow misses out on the fact that the OSS also didn't exist yet during Kerr's first time in Taiwan. Wang quotes a University of Hawaii professor, 鄭良偉 (Robert L. Cheng) who wrote (in a comment board post that is no longer available) that Kerr, who was living in an apartment overlooking Pearl Harbor, told Cheng that he often thought about how, with a heart full of righteousness and patriotism that let him overlook any danger, he went to the enemy territory of Taiwan, on the one hand to teach English, and on the other, to engage in secret field work to collect intelligence (滿腹的公義心及愛國心，讓他無視任何危險，前往敵國國境的台灣，一方面教英語，一方面進行秘密的田野工作，收集情報。) One problem with this statement is that in 1937, Taiwan (or even Japan) wasn't "enemy territory" yet, and unless Kerr was being anachronistic or had a bad memory by the time he talked to Cheng, he wouldn't have been motivated by Pearl Harbor in 1937.
The quote from Cheng in Wang goes on to say during the war, Kerr joined the US Defense Department and was sent to Taiwan. At the time he was publicly known as an English teacher, teaching at Taihoku Provincial College (which is now Taiwan Normal University) and many leaders in the Taiwan democratic movement (like Peng Mingmin) were students of his. (Wang notes in a footnote that Peng actually wasn't one of Kerr's students.) Kerr's "secret identity" was that of a member of US Naval Intelligence. (在世界大戰期間，Kerr以他的專長學識，投入美國國防部。他被派到台灣。當時他在台灣的公開身份是英語教師，任教於高等學校（現在的師範大學前身），許多台灣的民主領袖（如彭明敏）都曾受教於他。他秘密的身份是美國海軍的情報員。) This account is so totally confused that it's hard to imagine it appearing in a serious history book. It appears to be suggesting either that Kerr was in Naval Intelligence before the US entered the war or that he was teaching English in Taiwan during the time that the US was fighting against Japan. Either way, it's not only factually inaccurate--it's patently ridiculous. I seriously doubt that this came from a conversation with Kerr, unless Kerr was having problems with his memory (or Robert Cheng was having trouble remembering the conversation).
Note that I'm not saying that Kerr didn't make use of his knowledge acquired in Taiwan once he did join Naval Intelligence. I'm also not saying that it's impossible that Kerr might have passed some information on to the US government while he was teaching in Taiwan (though I'm guessing that they would have done better to use a "spy" who could actually speak and read Japanese and/or Taiwanese). But there's no real evidence, as far as I know, that Kerr was "sent" by the US government to Taiwan in 1937 to collect information, and the evidence that has been given in Chen's book is not much more than confused hearsay. The rest of her book seems to be well-documented, and I hope it's more believable than this part.
I have another problem with Chen's interpretation of Kerr's motivations for pushing trusteeship and later independence for Taiwan, but I don't have time to get into that. Suffice it to say that in my view, Kerr's motivations were probably more complicated and changing than what Chen thinks. (She seems to believe that he was totally motivated by his loyalty to the US and its interests.)
*I'm using "sailor" loosely here to refer to the fact that Kerr worked in Naval Intelligence during WW2.
**I know, awful translation of the title.