He also mentions the benefit of something invisible: In WWII the allies had to relearn the U-Boat lesson. Some people were arguing that the limited planes they have should be used to bomb more German sites, because they rarely spotted an U-Boat. However --- that was part of their effect: They forced the U-Boats to remain submerged for longer. (Those WWII-style U-Boats were essentially unchanged from WWI. Think of them as submergable normal ships, not as modern submarines. Their speed was severely reduced while submerged. The battery technology of the time was crappy and atom-powered submarines were a long way off. Surfaced they were somewhat faster than most merchant ships.)
Of course in WWII the breaking of the Enigma is closely related to the U-Boat war. And it's also in Tom Körner's book. With stories about Turing and Bletchley Park.
Edit: You can also tell an interesting story about Bayesian reasoning from the anecdote that when the aircraft crews reprogrammed the depth-charges to explode not where the U-Boat was most likely to be, but where the expected value of damage was maximized. And that meant closer to the surface: Most submerging U-Boats where already deeper by the time the charge hit, but those that weren't were mostly destroyed.
The end of (http://en.wikipedia.org/wiki/Battle_of_the_Atlantic_(1939%E2...) also has some things to say about convoys.
(And Tom Körner's excellent book "The Pleasure of Counting" has the math to back it up. He has a knack for explaining.)