"The very first Batman story, “The Case of the Chemical Syndicate,” was written by Finger and drawn by Kane. It was published in Detective Comics #27, which hit newsstands on March 30, 1939 (cover date: May 1939)." https://www.dc.com/blog/2019/03/19/batman-a-history-of-heroics-the-beginning
https://www.history.com/this-day-in-history/march-30/batman-comic-debuts-1939