USN gunnery performance at Empress Augusta Bay.

http://www.worldnavalships.com/forums/showthread.php?t=10171

From the discussion that went on in the thread linked above, it seems our Light Cruisers fired up to 4,000 shells during the battle, but only scored 20 hits, and while they got the job done, sinking the CL Sendai, the DD Hatsukaze, along with some additional damage inflicted on a few other Japanese ships, this was rather poor accuracy on the part of our cruisers, which as noted from some of the posters, might have been attributed to several factors:

• TF 39 commander Rear Admiral Aaron S. Merrill' efforts to keep his cruisers out of effective range from torpedo attack may have also put their guns at the edge of their maximum effective range, causing a larger slavo spread, thus reducing accuracy.
• Possibly firing continuously instead of firing in salvos and the resulting forest of shell splashes around the targets may have impaired the radar operators ability to locate them and determine their range; if this was a factor, then it seems the high rof of the Mk. 16 6" guns was more of a hindrance than an advantage for the USN in this battle.
• If the cruisers had been equipped with the older Mk. 3 fire control radar set instead of the Mk. 8, then the 2nd factor above may have been even more aggravated.

Despite this, however, Empress Augusta was still a decisive victory for the USN: They prevented the Japanese from threatening the Marines who had recently landed at Bougainville, had absorbed the lessons learned from previous battles and it showed in this engagement; last but not least, they sent a message to the IJN that they were no longer the masters of the night. Anybody else' thoughts on this?

 

It would have been interesting to see what would have happened if the Admiral in charge had assigned the US cruisers to fire on different targets. Everyone shooting at the brightest target was certainly not the best option. There was a fair amount to learn about how to use radar effectivly and this battle demonstrates that pretty clearly.

Looking at the stats on the US 6" gun at http://www.navweaps.com/Weapons/WNUS_6-47_mk16.htm
the ranges chosen looks like it would come close to maximizing the radial dimension of the salvo foot print. Longer range would shrink that component while increasing the azimuthal one but maximizing the chance of deck hits. Given the weakness of IJN cruiser turrets that might have been a better option. This page http://www.navweaps.com/index_nathan/Penetration_United_States.htm suggest pretty impressive deck penetration figures for the 6" gun at over 20,000 yards as well. Even the IJN heavy cruisers would have been vulnerable to deck penetrations at over 20K yards from what I can see.

 

If they fired in salvos, it might increase their chances of getting a hit.

What was the maximum effective range of the Mk. 16s'?

 

The problem likely wasn't the lack of salvo fire it was likely figuring out whose shells were off. If you are the only one shooting you can get a pretty good bead on it based on time of arrival but with everyone putting rounds on the same target telling whose splashes were whose is non trivial. Especially with the number of guns and rate of fire involved.

As for maximum effective range, how do you define effective? From the data I linked above from 20,000 yards out to max range even Japanese heavy cruisers were quite vulnerable to those guns. You do give up some P(h) when shooting at longer ranges but rounds that penetrate the deck or turret armor tend to produce significant damage especially if they detonate. Looking at it with 20:20 hindsight I think I would have probably tried to keep the range in the 22K to 24K band and assigend one CL to target the right most ship and work in if a change of targets was neccessary, another would have been assigned to do the same from the left the other two would start just left of center and work left and just right of center and work right. That way there's a good chance you get decent fire distribution. It would also be possible to tell who was shooting at who I think and specific reengagement orders could be given if it looked like one of the cruisers was not being serviced.

 

I don't think we ever learned effective fire distribution at night. As late as the Battle of Surigao Strait, the USN was still suffering from over-concentrating on a target.

Concerning Surigao Strait from: http://www.ibiblio.org/hyperwar/USN/rep/Leyte/BatExp/Leyte-BE-78.3.html#gunnery

 

During the Doolittle Raid, I've read that when the task force was spotted by the Japanese pickets, escorting US cruisers were ordered to fire upon and destroy them before they had the chance to relay the message of the US carriers being so close to home waters. Many rounds were fired before finally taking the pickets out, and this was in daylight if I remember correctly. The task force commander had the cruisers report for remedial gunnery practice once the mission was completed.

 

I believe that it was just USS Nashville which was singled out in the Nimitz's AAR for excessive expenditure of ammunition in destroying the patrol boats.

One mitigating factor would be the awful weather conditions at the time.

 

Yes, from viewing newsreels of the bombers taking off, the weather did look a little less than optimal conditions for shooting. Maybe Nimitz was a bit ticked off at the Nashville's skipper. Owed money from a poker game maybe?

 

Expending about 900 rounds to sink little Nitto Maru would be enough to tick off any of the top brass. Halsey was also less than pleased with the bombing accuracy of the aircraft also involved in attacking the pickets.

 

Good point.

By effective range, I mean the maximum range where the gun still has a reasonable chance of hitting its target, for example:

http://en.wikipedia.org/wiki/8.8_cm_KwK_36

1500 meters is the maximum range where the Tiger 1s gun still has a better than 50% chance of hitting its target under combat conditions using the PzGr. 39 APCBC round.

 

Would you say the lack of good fire distribution is also one of the contributing factors to the US Navy's defeat at Tassafaronga, Kolombangara, and Vella Lavella?

 

That really depends on what you consider a "good chance". British and German doctrine with battleships was to fight in the range band of 15,000 to 22,000 yards roughly (this is from memory so I may be off a few thousand yards) where the USN and IJN battleship doctrine was to fight in the range band from 24,000 to 30,000 yards. They acknowledge a low p(H) but thought the potential of more damaging hits was worth the trade off. The above was for the late 30's and into 41 I beleive. Radar allowed the p(H) at longer ranges to increase. If cruisers were following the same doctrine I see no reason for the effective range of the 6" gun not to be considered as anything up to max range. Note that Iowa was able to repeatedly stradle a DD at over 30,000 yards often with only 3 gun salvoes (a post a few years ago on the j-aircraft ijn board indicated that either she or New Jersey may have even inflicted splinter damage on the Nowaki at those ranges) which suggest that the battleship guns could be considered effective out to max range when engaging opposing battleships.

In regards to fire distribution at Surigao it is worth noteing that Oldendorf's battleships had been training mostly for shore bombardment from what I remember reading and not ship to ship actions much less radar controled ship to ship actions at night. I would have expected Lee's battleships to be a bit better in that regard. Although having the battlehips concentrate on the opposing battleship in that action wasn't necessarily a bad idea. The cruisers on the other hand should probably have engaged their opposite number or even the IJN DDs. As it was at least one US DD was hit by friendly fire though so perhaps that wasn't the best idea either.

 

It didn't help with accuracy that Merrill was executing radical evasive maneuvers and popping smoke to spoil Japanese aim when his batteries were firing at extreme range.

 

Well, "popping smoke" is irrelevant, as the US guns were under full radar control - The American cruisers never did spot the enemy at those extreme ranges.

Which brings up one thing I keep returning to...Was the Mark 8 up to the task of spotting 6-inch shell splashes at long ranges?

This source: http://www.eugeneleeslover.com/ENGINEERING/OP658_Fire_Control_Radar_Mark8.pdf
Tells us that the Mark 8 is able to spot 16-inch shell splashes on Type B scan with bith EXP and PREC sweep. But it says nothing about 6-inch shell splashes. Given that this radar spot smaller targets at reduced ranges, I can only conclude that it was not able to spot the smaller shell splashes at those extreme ranges. Thus the radar would be good for providing range, but was incapable of correcting the gunfire of the smaller gun calibers.

As has been mentioned, shell flight time is also a consideration as the 6-inch flight time at 20,000 yards is 44.7 seconds. A ship moving at 25 knots will cover roughly 629 yards during that time. Also, if the guns are firing at close to their RoF, there would likely be 4 shells per gun in the air when the first one landed. Thus gun laying corrections are not going to have an immediate effect on accuracy.

 

Not necessarily.

IIRC, Lee declined a night action during the Philippine Sea, because his battleships were not sufficiently trained in night combat, because they had been focusing on their anti-aircraft training. So, they were probably no better off than Oldendorf's OBBs in overall training, although Lee's battleships would have possessed better fire control and radars.

 

I thought the 3 of Oldendorf's that contributed most of the shells had the same gunnery radars and fire control systems as the Iowa's. I have read that Lee dedicated a significant amount of time to radar controled ship to ship gunnery practice. There was still a fair amount of variation between crews though as the Nowaki shoot demonstrated (Iowa was stradling or coming close on allmost all of her salvo's New Jersey not so much.

As far as detecting 6" splashes at 20K+ yards I wouldn't be in a hurry to make that assumption. Iowa and New Jersey were detecting splashes from their 16" guns at pretty close to 40,000 yards and the limit there may have been the radar horizon rather than the splash size. Note also that with range that if a target of size A can be detected at 40K yards then one would expect a target of 1/16 * A to be detectable at 20,000 yards.
On this page they (iowa) mention not having any problems spotting 5" shell splashes but they also mentione they had the Mk13 rather than the Mk8 fire control system:
http://www.navweaps.com/index_inro/INRO_BB-Gunnery_p1.htm

There is a lot of info on this page but I couldn't find anything definitive on shell splashes:
http://www.survivalebooks.com/free%20manuals/1945%20US%20Navy%20WWII%20-%20Radar%20Operators%20Manual%20%20%20408p.pdf
I would expect the splash from even a 6" shell to be greater than that of a plane but could be wrong there as well.

 

Not quite the same, they had Mark 34 directors with Mark 8 radar, modern BBs like the Iowas had Mark 38 and Mark 13. Mark 34 was first used in the Brooklyn class cruisers, so it was almost contemporary with Mark 38; hopefully someone can elaborate on the differences between them.

Mark 34 was used with 6", 8", 12", 14", and 16" guns. In addition to new construction, a total of 19 Mark 34s were fitted in older ships:

Reconstructed BBs California, Tennesse, West Virginia - 2 each
Pennsylvania, Maryland, Colorado - 1 each - these were fitted late in the war (after Surigao Strait) on short towers in place of the mainmast, the ships retaining their existing foremasts and forward fire controls, not the ideal arrangement but a quick-and-easy wartime improvement.
CAs Augusta, Chester, Louisville, Portland, Indianapolis - 2 each

The conversion of nine Cleveland class cruisers to CVLs put 18 Mark 34s back into inventory.

 

I did find a site that went into the details of the various radars but not sure where it was. Navweapons may be a place to start looking. Haven't found much at all on the ability to spot splashes of smaller caliber guns though.

 

Good Lord, 900 rounds you say! I think that Halsey was perfectly right to be discombobulated to say the least. With that much shooting, they should have accidently hit the Nitto Maru waaaay before that, or at least capsized her with splashes from near misses.

 

In fairness to USS Nashville, the rough seas on that day may have impaired her ability to hit the tiny craft.

http://es.wikipedia.org/wiki/Nitto_Maru_%281935%29