Hit a target from space, anywhere, in less than an hour.

[kgbsquirrel]

I think it would sink. 

I think in that case it would actually be a waste. It would through-and-through the ship (3/4" special treated steel would be so much tissue paper to this projectile) and then I would think lose alot of the energy to the water and the river bottom. At this point the ship sinks 30 feet and settles on the bottom. Salvage divers come in, patch the ship, refloat it, and haul it off for repairs.

On the other hand, if tests showed that the projectile would core the ship much like a APFSDS tank round, and then produces enough reflected energy off the river bottom to literally rip the ship apart, that would totally be worth it. Trading half million dollar (counting the lifting costs) tungsten darts for 500 million dollar ships? That's a win right there.

[Tallpine]

What about the can't remember the name of it meteor/comet that exploded over Siberia about 100 years ago?

How hard would it be to come up with a compound of materials that would spontaneously airburst at a designed altitude and speed ? 

[kgbsquirrel]

What about the can't remember the name of it meteor/comet that exploded over Siberia about 100 years ago?

How hard would it be to come up with a compound of materials that would spontaneously airburst at a designed altitude and speed ? 

The Tunguska event (is it sad that I pulled that from memory about 2 seconds after reading your comment?)

The problem with recreating  Tunguska is the hypothesis that said meteor/comet was composed of fissionable material that went critical due to heat and compression of reentry with a resultant explosion believed to be between 10 and 15 megatons. In this case we are trying to avoid using nuclear weapons. 

As an aside we already have things that do that. They're called W-53's.

[erictank]

What about the can't remember the name of it meteor/comet that exploded over Siberia about 100 years ago?

How hard would it be to come up with a compound of materials that would spontaneously airburst at a designed altitude and speed ? 

Tunguska.  ("God bless you!"  )

I'd think a "programmed airburst" for something like a crowbar would be quite difficult, myself - at that point, you're getting back to the complexity and expense of a nuke, which kind of negates the point of the crowbar (dead-simple cheapo KEW).  Besides, if you have to whack it with something bigger than a 30KT groundburst, you're in trouble anyways.

In order to dump all that KE into the air to create an airburst, wouldn't it have to turn almost instantly into REALLY tiny particles?  You're talking about putting a fair-sized explosive inside the crowbar, which isn't supposed to be all that big, and even then, I don't know if you'd get the shockwave or not.  You'd probably get a thermal pulse, but would it explode like a nuke when the internal explosion turned the 150Kg of rod into 1mm^3 tungsten shards and they melt and vaporize in the air at 7mi/sec?

[AJ Dual]

The charge may only need to shatter the crowbar just enough to let the atmosphere do the job. It's hard to say.

And the KEW dart could be pre-fragmented so that it's strong on it's main axis of travel, but does not have much lateral strength making the bursting charge needed less.

Although amazingly, it kind of points out just how BIG space is, even just the upper reaches of the atmosphere. Bolides are exploding with regularity in the upper atmosphere with various multi-kT yields all the time. (and few ever notice) It was a significant source of false positives for our early generation nuke test monitoring satellites.

[mellestad]

What about the can't remember the name of it meteor/comet that exploded over Siberia about 100 years ago?

How hard would it be to come up with a compound of materials that would spontaneously airburst at a designed altitude and speed ? 

Really hard.  And like Squirrel said, at that point you might as well just use a nuke.  And if you are going for deniability, I doubt it would work since it would be too easy to track the trajectory and show it wasn't natural.

[MechAg94]

http://www.foxnews.com/scitech/2010/04/26/falcon-hypersonic-missiles-project-aurora/
Looks like that second secret craft failed somehow after launch. 

But in a statement released Friday night, DARPA said that while “the launch vehicle executed first-of-its-kind energy management maneuvers, clamshell payload fairing release and HTV-2 deployment,” all wasn't perfect with the superfast craft. “Approximately 9 minutes into the mission, telemetry assets experienced a loss of signal from the HTV-2. An engineering team is reviewing available data to understand this event.”

The DARPA press release did not specify whether any of the test maneuvers were completed by the Lockheed Martin built craft before controllers lost communications with the craft, the site adds.

This was also in the article.  I hadn't heard some of this before.

In the real world, Project Aurora is called the "Prompt Global Strike (PGS) program" and it's actually part of the President's solution to maintaining peace in non-nuclear times. President Obama signed a treaty with Russian President Dmitri Medvedev last week that put both countries on the path to full nuclear disarmament.

However, the U.S. part of the agreement states that the country can replace every decommissioned nuclear weapon with a PGS missile. Within a week of the treaty being signed, Obama welcomed in the technology to make it possible.

And overnight, Obama announced he would support deploying a new class of hypersonic missiles that could hit any target on Earth within an hour.

[Tallpine]

Bolides are exploding with regularity in the upper atmosphere with various multi-kT yields all the time.

That's what I was thinking.  Not a nuke, just some mixture of mostly inert materials, but that would make it closer to the surface before exploding.

Maybe ice or water inside an iron shell?

Mostly just thinking... if nothing else, it would make a nice fireworks display