They are a good place to go for this kind of stuff.

Both Russia and China have made noises about missiles that would. The DF-17 appears to be the development platform for the aerodynamics. As well, it makes sense as a development direction for the land powers. Given the question was about why CN was so advanced, I answered from that angle.

https://jamestown.org/program/updated-chinese-hypersonic-weapons-development/
https://www.scmp.com/news/china/military/article/3023972/chinas-hypersonic-df-17-missile-threatens-regional-stability

“I thought they were using rockets shooting them high and then using gravity to get terminal speed. You could do this with ramjets to get the height then aim down to get terminal speed.”

Depends on the missile system. The question was about hypersonic missiles, not supersonic. Ramjets top out at around Mach 6, but really work best at slower speeds and need to be boosted to operating velocity before you light them.

You can get hypersonic with rockets, but then you have fuel mass issues. The current development target seems to be starting with a rocket first stage then switching to the hypersonic vehicle once you are fast enough to light the scramjet.

I think the high speed glider approach of the DF-17 is almost certainly an interim design. I’m not sure a glider would have enough cross-range capability to ensue hits in modern adverse conditions.

“It would seem to me that we could use a small .50 cal or so round fired very, very fast and with a horrendous volume of them shoot down these missiles. Anything, anything at all that hit one would blow it to pieces.”

I wouldn’t use the .50 cal BMG for this, that has less impact energy and range than you would like. Also, the problem with the indiscriminate-hail-of-bullets technique is it uses a lot of ammo, too much for a ship that needs to carry other stuff.

What has actually been done is similar, just more focused. eg. the US Phalanx and the NL Goalkeeper anti-missile close in weapon systems (CIWS). Phalanx uses the M61 Vulcan 20mm Gatling gun, often with depleted uranium sabot both for impact mass and so their tracking radar can more easily see where its bullets are going. Goalkeeper uses the 30mm GAU-8 Avenger Gatling gun from the A-10. Both of them have extensive sensor suites and fully automated targeting and firing capability along with very high rates of fire. Other modern navies have similar systems.

For the USN and allied sea powers, these are all part of a layered missile defence strategy. You have fighter aircraft out far, AEGIS missile ships closer in, and CIWS, chaff, etc. for terminal defence. Currently, the USN and allied navies are looking at stealth(y) ships as another layer in their defences.

Are they even using scramjets????

I thought they were using rockets shooting them high and then using gravity to get terminal speed. You could do this with ramjets to get the height then aim down to get terminal speed.

It would seem to me that we could use a small .50 cal or so round fired very, very fast and with a horrendous volume of them shoot down these missiles. Anything, anything at all that hit one would blow it to pieces.

Could be. It doesn’t really matter though as most of the technology is 50+ years old. The USAF was flying Hound Dog supersonic stand off missiles on the B-52 force since ’61 or so. The AS-4 was debuted in 1962. The guidance systems are from a bit later, but the ’60s F-111 had an early automated terrain following radar.

Probably the hardest part is building the scramjet engines which are needed to get both long range and high speed. The first known working scramjets were flown back in 1991 by the Russians and NASA participated in a some of the later development work.The Chinese could have bought it, they could have stole it, they could have independently developed it, or some combination of the above. There has been plenty of time, they are not stupid, and they have enough of an economy to afford to buy.

Doctrinal differences, mostly. I would also argue that it is actually the Russians who have the most experience in big and fast anti-ship missiles. They were a key part of the Soviet Navy’s plan to close the North Atlantic to NATO convoys during the Cold War. (eg. AS-4 ‘Kitchen’ https://en.wikipedia.org/wiki/Kh-22 and it’s successors) Correspondingly the United States Navy formed its doctrines for dealing with these missiles at that time.

The big and fast anti-ship missiles are only really suited for denying sea control to a competing power. They do not allow you to exert your own sea control by themselves. If you are primarily a land power like Russia and China, this is very attractive as full navies are expensive.

From the perspective of a sea power, such as the US, the Navy has a number of other missions and thus needs a different mix of capabilities to carry out those missions. Accurately or not, the USN believes it can use these other capabilities to defeat enemy navies without using big and fast anti-ship missiles themselves. The US could build such missiles if they thought it would be useful. The cruise missiles they have are a large chunk of the way there.

Those carriers too if carrying for instance a full complement of twenty or so F-35 VSTOL warplanes lack any sort of AEW, EW, tanker ASW organic. They too will be independent on land-based assets if again operating in the sea control mode.

The two ski-jump carriers the Chinese have are only interim designs. They are building Nimitz class (non-nuclear) carriers, which could carry the needed surveillance and AWACS aircraft.

The Liaoning and Type 001A look more like amphibious assault support ships than sea-control carriers.