Originally Posted by M21Sniper

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The USN funded two programs to develop a scramjet powered missile capable of point intercepts from the 1950s until 1986. The project "SCRAM" engine was succesfully tested in the late 1970s.

Scramjet technology is all about the engine, what the platform you put it in's role is has very little to do with the engine itself. Just like any other engine type...

Tell that to the typical M-1A2 gunner who can kill you over 2 miles away with an APFSDSDU 120mm main gun round....on the first shot, while you're both moving at 40mph.

"2. The HARP 16" gun was the longest in the world,100 Cal long (2 barrels welded together)"

It's also very old technology

"Longer barrel, longer time to build up to speed so lower forces on round compared to launching the same round from a conventional 16/50 to get the same range results."

Shockproofing has come a long way in the last 20+ years. So has miniturization, powder technology, metallurgical technology, and propulsion technology.

Hence the US Army starting a new collaboration for a 120mm scramjet powered tank round, and the USAF demonstrating a close to operationally useful sized(for the B-52) scramjet powered missile. Time for the USN to hop on board. It's not like it would be new for them, the funded scramjets for about 40 years.

And let's compare an ERGM with a 16" scramshell for a moment.

ERGM has a conventional sustained rocket motor, fuel, guidance, and warhead all stuffed into a 5" frame(albeit a long one). Because it needs rocket motor sustain to achieve it's specified range(oops, it doesn't come close to meeting it's range specs), it requires a lot of fuel.

A 16" scramshell would be able to dispense with the warhead entirely. The sheer KE generated upon impact ensures that it would be far more powerful than any amount of HE you could actually jam into a 16" round. That saves you about 150lbs right there vs a conventional HC round, and a lot of internal space.
By volume, a 16" round has what, 1000% more internal volume than a 5" ERGM round(wild guess, i suck at volume equations, lol)?

Finally, if you can make a big scramjet engine, you can make a small one. You do not need as much thrust to propel a 7 or 800lb low drag projectile as you do to propel a "12 ft long 5ft wide 2ft high 3000 lb vehicle", so you don't need as much engine. And all it needs is about a 10 second burn time to achieve the kinds of performance the eggheads are looking for. Even a 5 second burn time would triple the range of an equivelant ballistic projectile(Scramjets accelerate fast)

BTW, the only reason he compares HARP to modern rounds at all is to counter the Admirals shock damage claims. And he is quite right, the HARP project did loft sensitive electronics at extreme velocities, and they did prove capable of surviving the shock. And that that was decades ago.