This article in Asia Times adds to our understanding of nationalist elements in Japan politics. The writer's pro-China bias is so thick that even I could pick it up, but he makes clear the current [and maybe emergent] Japanese strategy: Aggressively patrols the Senkaku Islands as territorial waters, but not crossing the bright line of settling the islands. Japan's strategic concern is in not antagonizing Taiwan on the Diaoyutai issue, which can strengthen the pro-unification camp in Taiwan. [The independence movement in Taiwan is pro-Japan for historical and geo-strategic reasons.] If Taiwan ever reunifies, Japan will settle the Senkakus in a heartbeat.
More broadly, Japan's overtures to Vietnam, and Phillipine's ASEAN rebuke to Sec. Clinton's South Sea remakrs, underscores an interesting anti-colonial dynamic [for lack of a better word] at play in South East Asia. [The Hate Triangle that is North East Asia is well-documented.]
In all ASEAN states [except Singapore and maybe Brunei], there are strong sentiments and biases against both China and America. [A bit of Japan, too, but that's faint compared to the other two.] The Chinese outposts in the South Sea are sore spots to the surrounding countries, but their people don't like the Americans, either. For example, Vietnam would really prefer Russia over the US in balancing China, but Russia cannot do more than sell weapons at present. In fact, Russia wants to refurbish Cam Ranh Bay, but we'll see if it actually happens. Up Country portrays well both the strategic inevitability of a US-Vietnam security alliance, and Vietnamese reluctance to do so.
Phillippines has been pissed off about the American evacuation of Clark Air Base in 1991. Its intelligentsia are suspicious of America over its support of Marcos regime. Indonesia has regional aspirations, colonial baggage, past military dictatorships, and an Islamic identity, all of which build the above bias as well.
All this is to say that the US may have no "entry point" into a Battle of the South Sea. While the US has a freedom of navigation concern, the combatants (China + one more) will not want its help in resolving the battle. The most likely scenario is where the US Navy escorts neutral convoys together with Singapore and Japan, a la the Tanker War'84-88. The escort scenario will require several squadrons of FFGs, which the US Navy is retiring soon.
Most of the popular South Sea scenarios envision the US taking a combatant role against China's southern fleet, which in turn feeds into the general support for more destroyers and aircraft carriers. However, the political emphasis on the higher end of the Navy is unbalancing it for meeting the full spectrum of requirements. The combatant scenario is but one of the possible futures of the South Sea. Another equally likely future is the above escort scenario. Convoy escort is generally the duty of frigates, but we are coming up against a frigate gap. The current difficulties of the Littoral Combat Ships program means it may be cut short. It will take time to start up a replacement frigate program. So there may be a long gap between the retirement of the last Perry and the introduction of the next frigate, in the near future. If the South Sea Battle falls during this gap, the US Navy will have to commit our Aegis destroyer squadrons [which are national strategic assets for missile defense] for convoy duty, which is a much lower strategic priority. So the USN is on the trajectory toward a disastrous South Sea.
[The LCS as currently configured is completely incapable of convoy air defense, and only possibly capable of the convoy ASW, pending its ASW module.]
Another question we need to answer is the strategic priority of the South Sea itself. With the opening of the Northwest Passage, the South Sea is no longer the petrol lifeline of Japan. Australia, another ally, does not depend on the South Sea for petroleum. Other than the possibility of oil, and the general global commerce, why should the US care about the South Sea?
The popular South Sea combatant scenarios may be the manifestations of a US Navy in search of a strategic purpose. The continuing focus on a "near peer competitor", aka China, is unbalancing the US Navy from its other strategic priorities, as I outlined above. We need some sanity over this piece of ocean, at least in the US. That the ASEAN states go crazy over the submerged atolls there does not mean it will start World War III. The most important role for the US is to contain the conflict, and compartmentalize its effects from the rest of the world. With a robust convoy escort capability, we can minimize the harm of a shooting war on global commerce, and avoid foreign entanglements. The Senkaku flare up reminds us all that there are no easy territorial disputes left in the world. All of the remaining territorial disputes have no clear title holders; every claimant has a legitimate claim to the title. The rest of the world should not suffer from these petty title fights.