Over at the American Innovation blog, Matt does a an outstanding job of discussing how one would have to go about defeating China's anti-access strategy, a large part of which would be anchored by the S-400 (SA-21 "Growler") surface-to-air missile system. It is a well researched and well presented effort. Here is the salient part concerning why the 5th generation of aircraft are critical to any future strategy that involves A2 strategy given the sophistication of SAM systems these days:
The deployment of the S-400 would be problematic for the United States as 4th generation aircraft would be unable to safely operate near China (which is already the case but to a lesser extent with the S-300 PMU2 and HQ-9) but the USAF maintains the capability to overcome the S-400 with stealth aircraft. The LSR-B, B-2, F-22, and F-35 should all be stealthy enough to destroy S-400 sites if equipped with the right munitions. For example, the F-35 is cited to have a frontal radar cross section around .0015m^2 and a rear of .01m^2 (Global Security, 2011). Thus, the F-35 would be able to approach the 92N2E Grave Stone without being detected until 40 nautical miles (after weapons release the F-35 will have to turn around exposing the larger rear rcs hence 40 nm not 20 nm). If the F-35 is equipped with the GBU-39/B small diameter bombs (SDB) which have a stand-off range in excess of 60 nautical miles (Boeing, 2013), the F-35 is more than capable of getting the job done. However, the F-35 would be unable to use JDAMs to destroy S-400 sites as the stand-off range is insufficient. The Raptor is considerably stealthier than the F-35 with a frontal radar cross section of .0001m^2 with a side and rear of between .01-.001m^2 (Air Power Australia, 2011). Thus, the Raptor might be able to employ JDAM's against S-400 sites if it drops the 1,000 pound JDAM's from altitude and at maximum supercruise speed of mach 1.5-1.8 which gives a standoff range of at least 24 nautical miles (Hanlon, 2006). However, using SDB's would likely be preferred as it gives a much greater margin of safety for F-22 pilots.Unless we plan to cede the air near China to China, we had better have aircraft that can operate in the environment they're steadily building. Anything less and we may as well dump the "Pacific Pivot", or rename it the "Part of the Pacific Pivot".