Answer:
A "paper son" is a term used for young Chinese immigrants coming to the United States prior to 1944 who claimed to be a son of a citizen but were, in fact, sons on paper only.
The Chinese Exclusion Act of 1882 was the only law in American history to deny citizenship or entry based upon a specific nationality. The only immigrants allowed into the US were merchants, students, diplomats, and sons of citizens. Prior to the passage of this act, there was an open immigration policy to the United States.
The San Francisco earthquake of 1906 destroyed city hall which contained all birth records in San Francisco. As a result, thousands of Chinese men claimed to have been born in San Francisco and the US government had no choice but to accept their claims. Because of this loophole, Chinese men would travel to China and upon return claim marriage and the birth of multiple children.
While some of the births were legitimate, others were created as slots so that they could be bartered, bought, or reserved to bring other relatives to the US.
When a young Chinese boy attempted to enter the US as a son of a citizen, he was subjected to a rigorous interrogation by US Immigration Officials to determine if the applicant was a true son of a citizen. Many of these boys would have to memorize details of their life in China and these facts would need to match up with other interviews conducted, usually with the father and other witnesses. These records are stored in various Regional Archives of the National Archives of the United States.
After Pearl Harbor was bombed in 1941, sentiment towards Chinese in America turned more favorable. The Exclusion Act was eventually repealed in 1944 as an attempt to strengthen relationships with the Chinese government in the war against Japan. Chinese men were no longer subject to such interrogations although legal immigration from China to the US did not reach signicant numbers until immigration reform in the 1960's.