The Volokh Conspiracy - Lessons of Pearl Harbor:

An appropriate way to mark the 65th anniversary of Pearl Harbor is to reconsider one if its key lessons: the difficulty of predicting an enemy's strategy and tactics, and problems this poses for a primarily defensive national security strategy. As Roberta Wohlstetter showed in her classic study, Pearl Harbor: Warning and Decision , US intelligence actually had a great deal of evidence suggesting the possibility of a Japanese attack on Pearl Harbor even before December 7, 1941. In fact, the US, through its MAGIC program, had broken the Japanese military and diplomatic radio codes, and so was reading many Japanese communications in "real time." Yet US officials still failed to predict the attack in large part because the evidence pointing in the right direction was balanced by lots of other evidence suggesting that Japan would pursue other options (such as attacking the Phillipines, attacking British and Dutch possessions in the Far East while leaving the US alone, etc.). Only after the fact was the US able to separate what Wohlstetter called the "signals" from the "noise."

The 9/11 Commission report suggests that signals and noise issues also played a role in intelligence failures prior to 9/11, though we did not have as good intelligence on Al Qaeda prior to 2001 as the US did on Japan prior to Pearl Harbor.

As the MAGIC example dramatically demonstrates, there are serious limits to even the best intelligence. A reasonably smart enemy will deliberately send out contradictory signals and "noise" before any attack. This point applies with special force to modern terrorists, who have a large number of potential targets to choose from. Sooner or later, they will catch us by surprise again.

For these reasons, among others, we cannot win with a purely or even primarily defensive orientation. Ultimately, we have to engage in offensive operations, in order to destroy the enemy before they are able to implement their own attack plans, and so we ourselves can exploit the advantages of surprise and confuse the enemy's own intelligence. Offensive strategies certainly have their own risks, and are not a panacea. However, even more than 9/11, Pearl Harbor demonstrates that an exclusively defensive orientation is a guarantee that our enemies will take us by surprise sooner or later - with potentially devastating results.

UPDATE: Many of the commenters have, perhaps predictably, immediately gone into a debate over the Iraq War. The point of this post is both broader and narrower than Iraq. Narrower because the balance between offense and defense is just one of many factors that needs to be considered in assessing the decision to overthrow Saddam Hussein. Broader because the point of the post applies to other conflicts too. In particular, it applies to the debate between those who believe that we can best counter terrorism and other threats through defensive "homeland security" measures and those who believe in a more aggressive offensive approach. In my view, the former strategy is likely to break down over time because 1) the enemy has an almost infinite range of targets to pick from, making it difficult to predict which one they will hit, and 2) the "signals/noise" problem ensures that we will periodically have intelligence failures similar to Pearl Harbor - especially if we don't have information comparable in quality to what MAGIC provided back in 1941. Does that mean that offense is a once size fits all solution to all national security threats? Of course not. But it's an important point to consider that I think is too often ignored.

	[Ilya Somin, December 7, 2006 at 9:12pm] Trackbacks Lessons of Pearl Harbor: An appropriate way to mark the 65th anniversary of Pearl Harbor is to reconsider one if its key lessons: the difficulty of predicting an enemy's strategy and tactics, and problems this poses for a primarily defensive national security strategy. As Roberta Wohlstetter showed in her classic study, Pearl Harbor: Warning and Decision , US intelligence actually had a great deal of evidence suggesting the possibility of a Japanese attack on Pearl Harbor even before December 7, 1941. In fact, the US, through its MAGIC program, had broken the Japanese military and diplomatic radio codes, and so was reading many Japanese communications in "real time." Yet US officials still failed to predict the attack in large part because the evidence pointing in the right direction was balanced by lots of other evidence suggesting that Japan would pursue other options (such as attacking the Phillipines, attacking British and Dutch possessions in the Far East while leaving the US alone, etc.). Only after the fact was the US able to separate what Wohlstetter called the "signals" from the "noise." The 9/11 Commission report suggests that signals and noise issues also played a role in intelligence failures prior to 9/11, though we did not have as good intelligence on Al Qaeda prior to 2001 as the US did on Japan prior to Pearl Harbor. As the MAGIC example dramatically demonstrates, there are serious limits to even the best intelligence. A reasonably smart enemy will deliberately send out contradictory signals and "noise" before any attack. This point applies with special force to modern terrorists, who have a large number of potential targets to choose from. Sooner or later, they will catch us by surprise again. For these reasons, among others, we cannot win with a purely or even primarily defensive orientation. Ultimately, we have to engage in offensive operations, in order to destroy the enemy before they are able to implement their own attack plans, and so we ourselves can exploit the advantages of surprise and confuse the enemy's own intelligence. Offensive strategies certainly have their own risks, and are not a panacea. However, even more than 9/11, Pearl Harbor demonstrates that an exclusively defensive orientation is a guarantee that our enemies will take us by surprise sooner or later - with potentially devastating results. UPDATE: Many of the commenters have, perhaps predictably, immediately gone into a debate over the Iraq War. The point of this post is both broader and narrower than Iraq. Narrower because the balance between offense and defense is just one of many factors that needs to be considered in assessing the decision to overthrow Saddam Hussein. Broader because the point of the post applies to other conflicts too. In particular, it applies to the debate between those who believe that we can best counter terrorism and other threats through defensive "homeland security" measures and those who believe in a more aggressive offensive approach. In my view, the former strategy is likely to break down over time because 1) the enemy has an almost infinite range of targets to pick from, making it difficult to predict which one they will hit, and 2) the "signals/noise" problem ensures that we will periodically have intelligence failures similar to Pearl Harbor - especially if we don't have information comparable in quality to what MAGIC provided back in 1941. Does that mean that offense is a once size fits all solution to all national security threats? Of course not. But it's an important point to consider that I think is too often ignored.