American battleship guns

[Saltheart]

When the Americans built the North Carolinas and South Dakotas they fitted 16 inch 45 calibre weapons. These fired heavy shells at low velocity to penetrate a lot of deck armor at very long range. This was in accordance with their doctrine of attacking their enemy at great range and destroying him by penetrating the deck armor over the vitals.

However when they built the later Iowas they fitted 16 inch 50 calibres that had a higher muzzle velocity and less armor piercing performance at long range with plunging fire. According to their battle philosophy of seeking long range anti deck engagements they had now actually regressed in firepower and fitted less powerful weapons to the Iowas than they had to the previous classes. Why this backwards step?
After all with ever improving radar you'd think they'd be more confident about long range engagements and be wanting to maximize deck penetrating power more than ever.

Was it that in reality they had come to the conclusion that close range engagements were far more likely and actually getting hits was far more probable at closer range and as a result had elected to go with a gun with better performance against gun turret faces and main armor belts than against decks? If so does this mean their philosophy had actually changed and is it the reason that the weapons actually more effective for their original deck hitting philosophy, the 16 inch 45, had been abandoned?

[frontkampfer]

Just a WAG on my part but did they think they (the Iowas') would be used more for bombardment of shore targets?

[alecsandros]

According to Friedman US batleships, BuOrd opted for a higher probability of hits at any likely battle range (up to 27km), in exchange for a lower number of truly devastating hits (through the deck armor).

The reason is that a higher m-v gun has a flatter trajectory than a lower m-v gun, thus assuring a larger danger zone on a given target.
More details here:

viewtopic.php?f=36&t=2631

[Saltheart]

According to Friedman US batleships, BuOrd opted for a higher probability of hits at any likely battle range (up to 27km), in exchange for a lower number of truly devastating hits (through the deck armor).

The reason is that a higher m-v gun has a flatter trajectory than a lower m-v gun, thus assuring a larger danger zone on a given target.
More details here:

viewtopic.php?f=36&t=2631

Alright so they didn't change their doctrine, good to know.
Thanks for the link, very interesting.

[Saltheart]

Just a WAG on my part but did they think they (the Iowas') would be used more for bombardment of shore targets?

I don't think so. After all the old battleships could do shore bombardment just as well as the new ones. I think they still believed the Japanese might somehow one day get battleships through to the US carriers and powerful US battleships would have to intervene. Maybe the fast Iowas were still that final line of protection.

[Thorsten Wahl]

due to the flatter trajectory and higher velocity the inner zone of immunity (Belt penetration is pushed out by approximately 4500 yards for the same vertical target thickness.

The same reason (flatter trajectory) results in a lower impact angle at deck targets at the same distance, so the outer zone of immunity for same deck thickness is pushed out, but only by approx 2000 yards
as the projectile fired from the 50 cal gun has approximately 160 fs more speed at 20000 yard and 80 fs at 30000 yard wich i would consider as most relevant battle distances regarding penetration and firecontrol abilities

[lwd]

I've also seen some stats for reduced propellant charges for the Iowa's giving them MV's similar to the 45 cal guns. If used at 30,000+ range out to max range for the 45 caliber gun this would give them the benefits of the 50 cal at closer ranges plus some (probably questionable extremely long range options) and the deck penetration of the 45 cal at longer ranges. I don't know when this was proposed or if they ever test fired the guns with these loads.