Commentary Negotiated in secret and sprung on the world last week, Australia, the United Kingdom, and the United States have created a new defense pact that is a direct if unspoken challenge to the growing Chinese military threat in Asia. Dubbed AUKUS (or, more awkwardly sometimes, AUUKUS), its immediate goal is to create a framework for transferring technology to Australia so it can build and operate nuclear-powered attack submarines. Australia currently possesses six conventional—that is, diesel-electric—Collins-class submarines but wants to replace them with 12 new submarines, beginning in the 2030s. Diesel-electric submarines are quiet and effective, but they are also limited in how long they can operate submerged. They must frequently surface and run noisy diesel engines in order to recharge their batteries. Modern conventional submarines are being supplemented with various “air-independent propulsion” (AIP) systems such as fuel cells, but they are still inferior to nuclear-powered submarines. Nuclear-powered submarines, in …