Along with interrogations of captured al-Qaeda fighters, communications intelligence (known as COMINT, in the intel trade) is one of the keys to American self-defense. Congress has long recognized the critical nature of this brand of intelligence. In the aftermath of World War II, it protected American activities in this realm in a special statute, Section 798 of Title 18, which makes it a crime to publish classified information pertaining to COMINT.

With the Bush administration’s failure to prosecute the editors and reporters of the New York Times, who in 2005 compromised one of America’s most critical programs for tracking al-Qaeda communications, Section 798 seems to have lapsed into desuetude. Evidently, the political costs of carrying out such a prosecution were deemed too great, and the benefits to national security, when weighed in the balance, insufficient.

In the wake of the Times’s disclosures, it is impossible to say whether al-Qaeda operatives became more careful than they already were in their use of emails and telephone communications. But that would be a logical supposition.

Whether or not that is the case, it is worth taking note of a chapter from a different era, when one of the world’s most evil regimes was carrying out its most evil deed—the extermination of the Jews. Eavesdropping on Hell is an authoritative account, produced by the National Security Agency, of what was learned about the Holocaust from COMINT as it was unfolding.

It appears that the Nazis, acutely aware of the price they might pay for their actions, were highly disciplined in their approach to using radios and other vulnerable means of communication. The result was that:

Allied communications intelligence discovered nothing of the prewar and early wartime high-level Nazi planning for the general campaign against Europe’s Jews and other groups targeted for elimination. This situation also was true for most of the large-scale wartime plans, such as the massacres in the western Soviet Union or the death camps. There were [a] few exceptions to this trend, most notably the intercept and decryption of German police messages that indicated that Italian Jews were soon to be subjected to roundup and deportation to camps in October 1943. Usually, though, Nazi planning, preparations, and orders to carry out these operations were not communicated in a means such as radio that could be intercepted by the Allied monitoring stations. Plans and orders were delivered by courier or were communicated orally at meetings and thus denied to Allied monitors. As a result, information that could have warned of an impending operation was missed.

The entire study is a demonstration of the vital importance of COMINT and the consequences of its absence.