There was never an indictment, because it was determined that this would serve to alert the Japanese that their codes had been broken, but what was interesting to me was that, 70 years after the fact, the government was still trying to keep this cloaked in secrecy:

Newly published documents by the National Security Archive reveal why a grand jury refused to prosecute a Chicago Tribune reporter during World War II for a leak.

Correspondent Stanley Johnston was accused of revealing the United States cracked a Japanese code, which alerted the military to Japanese war plans before the Battle of Midway. A Tribune editor attributed the source of information to “naval intelligence.”

A prosecution was contemplated under the Espionage Act, but the government backed off because they feared what may happen if a trial publicized that the U.S. compromised the Japanese code.

The Justice Department under President Barack Obama fought against a lawsuit filed by the Reporters Committee for Freedom of the Press. It lost when a district court ruled in 2015 that disclosure would “result in a more complete public record of this historic event” and affirm the government is “open, in all respects, to scrutiny by the people.”

Yet, the government appealed, and it was not until September 2016, when the appeals court ruled against the government’s claim that a federal court had no jurisdiction to order the release of transcripts, that an effort to keep 75 year-old documents secret came to an end.

This is a 75 year old secret, and Barack Obama and his Evil Minions^™ felt compelled to keep it under wraps, because ……… Worst Constitutional law professor ever.^™

One would think that Obama was working for the US state security apparatus, not the other way around.