Why Gun Ammo and not Cruise Missiles for the Zumwalt?

[KenV]

I seem to recall that the 155 caliber weapon.....

Naval guns use a different nomenclature than field artillery. In naval guns "caliber" is the length to bore ratio. So the 5inch 38 caliber weapon of WW2 and after has a shorter tube than the 5inch 54 caliber weapon of the cold war years, which in turn has a shorter tube than today's 5 inch 62 weapon. Zumwalt's Advanced Gun System (AGS) is a 155mm (6.1 inch) bore and 62 caliber long and is water cooled to support a high rate of fire. And oddly enough, the AGS ammunition is NOT compatible with the Army's/USMC's 155 howitzer. For one thing AGS reportedly uses a binary munition (separate projectile and propellant charge) Also, the howitzer ammunition's propellant cannot pass the Navy's insensitive munition requirements for ship board use. It took a few years before AMRAAM was available to the fleet for the same reason: the rocket propellant did not meet USN requirements.

[msbbarratt]

Also, the howitzer ammunition's propellant cannot pass the Navy's insensitive munition requirements for ship board use. It took a few years before AMRAAM was available to the fleet for the same reason: the rocket propellant did not meet USN requirements.

Similar situation in the UK. The RN came under some pressure to fit the 155mm from the army's AS-90, to make economies through ammunition commonality. The AS-90 also uses a binary munition, whereas the RN has had cartridged rounds for some decades now.

I think this was rebuffed - Wikipedia suggests that the Mk8 naval gun is still fitted, and reports (ironically) that it was cancelled due to budget cuts... It's far harder to store seperate propellant bag on ships: it's there for months, it can get damp, etc. The last thing you want on a ship is the magazine becoming dangerous simply because the aircon plant has packed up and the humidity has risen. One can ultimately lose a ship that way - expensive. On a self-propelled gun it's stored for a few hours at most, they can get rid of it quickly by throwing out the back, and even then they're pretty careful about keeping it in closed containers, etc.

[Lonewolf_50]

@KenV: thanks for the update. My era of understanding was back when the Army was working on a 155 system that would change how ammo and propellent was used: two inert agents in separate tanks (IIRC in gaseous form) that only met during firing. They were trying to get the Navy to agree, since that mode would make ammunition explosions on board less likely due to both being inert separately. ( This was about 20 years ago). I had since lost touch with that Joint proposal, though I had heard from my Field Artillery POC in the early 2000's that the Army did not end up going with that propellant choice in the end. (Memory foggy, have slept and had a few beers since back then .. and speaking of beer, we will miss Wurstfest this year. Arrggh. )

[KenV]

Lonewolf, I have a vague recollection of those plans. If memory serves the two-part propellant idea was grand from the perspective of preventing explosions, but the stuff was both corrosive and toxic. In the end the negatives outweighed the positives and the idea was abandoned for much the same reasons that hypergolic fuels were abandoned by the Army and USN. USAF uses hydrazine in their F-16s. The presence of hydrazine was one reason the F-16 could never make it to a USN carrier deck and why (among other reasons) the YF-17 was chosen by USN over the YF-16. The YF-17 then became the F/A-18.