In Comments Anonymous [Dec 18, 8:49AM] asked “I was wondering whether you would comment on a recent story that a Chinese submarine conducted a simulated attack on a CVN. What would in your view constitute a simulated attack from a submarine?"
The failing of these two American sources is assuming the waters in the area are only populated with US and Chinese vessels. These waters are (probably) the waters most congested in the world with submarines from South Korea, Japan and Russia. The waters are also congested with undersea sensor possibilities. So it is much more than a USN vs PLA-N vessel wargaming scenario.
It has been reported that the aircraft carrier, USS Ronald Reagan (late October 2015) sailed from the south, through the Tsushima/Korea Strait, north into Sea of Japan. The Chinese submarine may well have been already in (moving slowly) in the Tsushima Basin (Sea of Japan) as attempting to follow Reagan (at 20+ knots) might be too untactically noisy or impossible (for an SSK) at 30+ knots.
It is strongly assumed a Japanese Soryu class or Oyashio class submarine is deployed in the Tsushima/Korean Strait at all times.
It is highly likely that a South Korean Type 209 or Type 214 submarine would also be in that Strait for several reasons including keeping an eye on the Japanese sub.
Either the South Korean or Japanese submarine may have detected the presence of the Chinese submarine first - then informed via satellite Command Centers in Seoul or fleet HQ Busan and/or Tokyo or fleet HQ Yokosuka naval base (or copied in all of them). Message realtime relayed to Washington DC, USS Reagan and Reagan's surface escort(s) and a US SSN in the area of Reagan. The US SSN may usually be home based at Guam. The surface escorts and SSN may have separately detected the Chinese sub.
Other platforms may have detected the Chinese sub including P-3 or P-8 patrol aircraft with sonobuoys, ASW helicopter with dipping sonar, Tsushima Strait's possible undersea sensors, or a combination of several platforms.
A simulated missile attack from a Chinese submarine on USS Ronald Reagan?
The certainty of a missile simulation might be defined by default as "out of range of torpedos" eg. in Klub/Sizzler ASCM range but out of known Chinese torpedo range.
The simulation may have perhaps begun with a Chinese satellite or Chinese naval base 1. sending targeting information and orders (S Korea, Japan or US picking up traffic) on VLF or ELF radio frequencies intendeed for the Chinese sub.
Presence of Chinese submarine may include:
2. sonar feedback off the hull revealing sea-space location
3. electronic emissions (eg. mast mounted fire control radar) voices, mechanical sound from/in the
4. opening torpedo tube hatches
5. flooding torpedo or cruise missile tubes (less likely as this may be too close to an imminent launch)
6. Chinese submarine surfacing in vicinity of the Reagan, if Chinese Captain assumes his simulated
attack has, so far, gone undetected (eg. against carrier USS Kitty Hawk in 2006).
An out of sequence combination of any or all of 1 to 5 and maybe then 6. Even only 1. and 2. may together have been enough evidence.