Wow the discussion seems to have moved quite a bit.
1. DF 21a is an anti ship ballistic missile but is it an aircraft carrier killer?
Answer is NO. In navy when the Carrier moves it does not move as a lone wolf. It is supported by 2-3 GMD, 2-3 GMF, 2 SUBS, and a replenishment ship. Now mostly the missile picks up the designated target( the a/c ) by the electronic signal produced by it and upon re entry into the atmosphere guides itself to this ELECTRONIC SIGNATURE. But under operational condition one of the other ship mostly the frigate ( less important asset ) mimics the electronic signature of the a/c. There by confusing the missile and forcing it to attack the frigate mistaking it as the a/c.
What gets detected gets targeted too. There is no way a CBG will not be detected, triangulated and targeted from a combination of Satellites, planes, Subs and Ships. Missile does not have to pick up the CBG by the electronic noise it creates.
Electronic signature is just one solitary part of the kill chain. There are simply too many ways of targeting a CBG. There is a reason why most of the USN-CBGs just stay home, most of the time, while their bete noire mostly disregarded the CBG concept.
Multistatic Sonars work best against the whole circus of ships travelling at very high speeds making the most amount of noise possible. And the Chinese subs, even the ones about to fall off, on account of old age, will be able to carry some cutting edge sonars. There may be some doubt about the capability of these older subs to attack a CBG, but they will nonetheless be able to provide persistence in detection, triangulation and targeting aspects of the kill chain.
Not being alone is the main cause of a CBGs detectability. The paradox of defence and detection. Had the AC traveled alone it would have reduced chances of defence but better chances of stealth given its aircraft ranges. Like the way we hid our own INS Vikrant in 71 which was to be protected from an on-lease PNS Ghazi.
And US Navy has tried the electronic signature reduction in a CBG wide basis. They failed. 10 thousand men, multitude of equipment. Some or the other signal will always slip. And that is what the HALE UAVs would be sniffing out all the while for like 10s of hours of on station flying at say 250 knots an hour to cover at least 100 hours of the CBG travel route at any given point in time.
Then there would always be Satellites and recon aircrafts with radar &/or IR &/or optical sensors, reliant on the line of sight. The horizon to detect a CBG from an aircraft at 30000 ft is around 250 NM. Running at 30 knots the CBG while creating the most amount of sonic and electronic noise will take 8 hours to cover that distance of 250 NM in order to lose the pursuing aircrafts. Unfortunately for the CBG the recce aircraft will itself be flying at 450-750 knots plus, per hour for say say 8 hours of on station time and hand over the bearings to the other assets before retiring from the hunt. How much time will it take to scan the ocean from 30000 ft
. Satellites stay for only a few minutes but from those heights and at the scan rates possible they also can detect much larger swaths of the ocean than any other asset.
Should the AC dare launch its own aircrafts then you don't even have to detect the CBG, you just have to detect the aircraft and the CBG will about 2 hours away.
Then you can also track the underway replenishment ships.
2. Accuracy.
When a ballistic missile is launched it is guided to its target by either ring laser gyroscope or inertial. There is very very less chance to steer the warhead from its already predesignated target upon re entry. Now if the target is stationary like in land or during test launches it is not a problem. But during war time scenarios the a/c is moving in any arbitrary direction. Rendering the ballistic missiles useless.
Here the cruise missile plays a better role because of mid course and terminal course correction. So when you want to kill an a/c use your cruise missiles. The DF 21 is also equiped with terminal radar guidance but its efficacy questionable.
To get the obvious out of the way. Howsoever fast the CBG or the AC moves around, whatever pakdam-pakdai they try they cannot outrun a lousy subsonic cruise missiles, let alone a fast moving steep diving MaRV or Quasi Ballistic PBV. Esp. in a day and age where a foot print of a missile is in 10s of kilometers. Presuming a steep dive right from the 350 km Apogee of Agni-3 (longest vertical distance that an RV can travel) the RV will take 130 seconds (@ ~8 mach). During this time a CBG would have travelled 0.015 km at fastest straight line distance. Do you really think a modern RV will not have that kind of footprint.
On what is possible:
Pure ballistic went out of fashion some decades back. Over the years US has studied about 30000 variations of deliverying a warhead to its target and identified 30 concepts finally. Kalam saab had to look at 180 variations of just Agni-TD he was leading, despite the much better computing resources he had at his disposal. If you are presuming the old wives tales of ballistics that has been going around for about 2 decades now then you cannot be helped.
When a Chinese and an American meet on the net both talk about possiblities based on things already done and disclosed. But when these Chinese and Americans come to talk with Indians they keep quite. Mostly they would like that Indians keep hanging onto the old wives tales.
If a cruise missile can take mid course and terminal corrections what is to stop an RV on a ballistic from taking the same inputs. Only times ballistic courses cannot be corrected are a small window where the RVs are entering the atmosphere. At that point management of thermal and atmospheric shock becomes paramount and things become somewhat difficult to manage.
Multiple MaRVs on ICBMs have already been tested multiple times - these are only the disclosed instances and disclosed only by the US. Most other countries do not even disclose things. We ourselves keep testing Prithvis even today. Somebody has got to explain the surfeit of Prithvi tests. Our own people keep talking about 'single digit accuracy' for Agni-V class, which is suspected to be of 8000 km range by the Chinese who are the prime target of it.
The belief that Ballistic course missiles are not suitable for mobile targets is a belief that stands not because of do-ability of it. The belief stands on a very different reason. Because nobody has expressly disclosed that they have this capability, till the Chinese broke their silence. Prior to the Chinese only the US had disclosed the full capacity of their missiles like Pershing-2, but mind you they disclosed their concepts full 3 decades before the Chinese. Even this disclosure by the US came much after they had already perfected considerably better designs. Are we safe in presuming that the world stood still after Pershing-2. Chinese are being very truthful in stating their capabilities and that is why India is taking their developments seriously. Anti Ship Ballistic missiles have also been tried by the Soviets but they reportedly gave it up to meet treaty constraints and probably because they figure their Kh-22s could be developed to nearly the same exacting requirements - large warhead at 6 machs in steep dive mode. Today the dives of Russian missiles have become so good (65 degrees for Brahmos) that their is little practical difference from a defenders PoV whether he is hit by a cruise or a ballistic or a quasi ballistic hypersonic warhead.
Only difference, for a defender, that really remains is what velocity can be achieved at what ranges with what trajectories. It is in this context that the Ballistics serve the best. Because of mother nature. Even the current hypersonic vehicles that they are talking about are designed for either aircrafts or for Ballistic missiles that can provide a leg up to a post boost vehicle.
This disbelief about ballistics is like the CEP confusion, where the Indians claim single digit accuracy but the others rarely do. Does that mean others cannot our CEPs - off course no. Its just that it was the Indians who broke the silence most vociferously. Prior to us, others just used to mention it in paid articles and closed door seminars.
To be able to understand what most likely is true you will have to challenge your own presumptions and test out your own existing knowledge.
3. Warhead. Will DF 21 use conventional warhead or nuclear while targeting an A/c? Aircraft carriers are probably the costliest military asset of a nation. They have squadrons of aircrafts on them and sinking one of them will result in huge loss to both life and money. This is why they are also the most well built. They are practically most difficult to sink. A ballistic missile with a conventional warhead can NEVER SINK an A/c. You need a nuclear warhead to BARELY damage an aircraft carrier.
Please refer OPERATION CROSSROAD BY US NAVY. They detonated a nuclear warhead under codename Able to see their effect on the ships including 2 ww2 aircraft carriers. They were USS Saratoga and USS Independence. The resulting detonation was of 21 kt but they missed their targets by barely barely 650 mts and both aircraft carriers didnt sink! Though they suffered extensive damage due to fires caused by oil storage in both ships.
It is calculated to sink an a/c you need a minimum 100 kt warhead and within 500 meters from target. Coupling this with the fact that accuracy against a moving target is dubious, using both conventional warhead or nuclear warhead is waste.
OPERATION CROSSROAD is nearly 3 QUARTERS OF A CENTRURY OLD test . Good morning Rip Van.
But more seriously (hope you din't mind the pun above) you are presuming either of the following two:
1) that Nukes will be deployed. But Soviets gave up that route even though they had the best capacity to take the retaliation; or
2)that to take out a CBG the Chinese have to be cooperative with the US Navy. It is a USN scenario that the Aegis will protect the CBG.
My presumption is that the AC and remnants of CBG itself will be engaged by PLANs subs and long ranged cruise missile carrying Harbins under the cover of a large number of their land based or Laoning Sukhois.
All this after the Aegis itself has been taken out by a number of DF-21D. Till now Aegis has shown capability to take out only the Supersonic missiles in dive mode. DF-21D RV will be hypersonic in a very complex trajectory ending in a dive at 8 machs.
4. Using nuclear warhead against an already nuclear armed state.
Both China and India are nuclear armed state. The act of using a nuclear warhead against an a/c will result in a nuclear war which i hope both countries won't like to happen especially when their is so little to gain and much to lose.
About the nukes. I am dead sure nobody has the guts to use it. Ok perhaps the Pakis and Noko. But seriously the Nuke-5+India+Israel+Brazil+Soko+Japan have spend the better part of last half century making sure that they do not end up using nukes. Safing technology is one of the highest forms of Nuke tech for this reason alone.
Nako bai, no nukes. Its Haram.
Unless off course......
As I said all sides had nukes in their arsenal yet all sides gave up nukes and started pursuing conventional warheads on IRBMs and US already has conventional warheads on ICBMs. In US the debate centers around the aftermath of declaring that they are going to use conventional warheads on ICBMs for quick global response. Despite being the 'self declared boss of the world' they themselves are not confident of admitting to already have fielded a weapon. There was some talk that they would give advance warnings to Russians and launch from outside US or from the coast of US (Nuke laden ICBMs being presumably stationed towards the center of US).
5.Tests of DF21 and operational preparedness.
DF21 is still in research phase though Chinese media claim it is operational. But the lack of repeated test and lack of proper targets for those tests puts the claims into doubt. Chinese media are controlled by the goverment and often helps to propagate messages which are baseless and false.
Thus i feel that DF 21 will never be an aircraft carrier killer.
Feelings do not matter.
And lack of repeated tests could also be an indicator of confidence. AFAIK the Agnis were supposed to be tested a mere 3 times (others had marked 5 test limits for themselves) before declaring that a version of Agni can be handed over for operational tests. Have you given thought to the possibility that the Chinese already had this technology before 2010 and the tests were for the rest of the cards in the kill chain, to fall in place.
Pakis have not failed ever
but that is another matter.