Regarding the second attack on London's mass transit system Wretchard at Belmont Club makes this set of observations:
If the Economist is correct about the failure of the detonators to produce a high-order explosion two things can be inferred. First, the close-in defenses of London's public transportation system failed; after all the bombs were delivered to the trains and detonated, except that the detonations themselves were faulty. Second, the outer-ring of defenses, the anti-terrorist component that attacks the terrorist infrastructure, denies it havens, reduces its funding and makes it difficult to place competent bomb-makers in London has succeeded -- at least in this case. More details will clarify the situation as further news becomes available.
(Speculation alert) When faced with the suicide attack problem (Kamikazes) during the Second World War, US fleets adopted the concept of the layered defense around battlegroups, consisting of attacking enemy airfields, providing a radar picket on enemy lines of approach, creating a combat air patrol to intercept incoming Kamikazes and then presenting a succession of long, medium and short-range antiaircraft fire, before finally falling back on warship evasion, armor and damage control. Each component in the defense contributed its statistical share of the defense. The debate surrounding the prosecution of the war on terror can be conceptually split, though not very neatly, between those who advocate a layered defense with a forward-deployed component (coordination with 'friendly' Muslim countries, involvement in Iraq, Afghanistan, the Horn of Africa, etc), plus everything in between, and those who would rely primarily on terminal or close-in defenses (national IDs, CCTV cameras, border control, etc) in the homeland.
A small percentage of policy advocates believe that a complete reliance on nearly passive close-in defenses ("support the troops, bring the boys home", build bridges to Muslim communities, etc) would be adequate to protect the public against terrorism. Over the coming years, the value of every aspect of the defense will be highlighted by different incidents. Some attacks will be stopped by an alert security guard, others will be pre-empted in a land so distant the public will never even know that the attacks were mounted. But they are all needed. If any lives were saved in London today, it probably means that a deep defense makes a difference.
Defense in depth is such an obvious principle that it should be insisted upon by everyone, yet some on the current political landscape simply fail to comprehend its necessity. We are at war against kamikazis far deadlier than the Japanese pilots and our defense needs to be both long-range and close-in. To urge one without the other is astonishingly myopic. To depend upon one without the other would be folly.
