From: 20 yrs ago - SDO -> med down, w/BC glasses on
Here I was thinking I had a good grasp on the principal theories behind anti-aircraft guns. Then I read a couple posts have me scratching my head.
First off, I strongly suggest you some guys dive into this document if you haven't already before:
This document spurred many other tactical documents that will never be declassified. Some of the conclusions contained within it are off the mark but the data being presented is most telling about the nature of engaging aircraft with hot flying lead. Pay very close attention to the charts located in the back.
To address some of your posts:
Not sure why you'd be interested in the time between reloads on any AA gun? Besides, I'm sure at least 1 or 2 of the guns you've listed can vary their rate of fire (ROF). Only the EFFECTIVE cyclic rate (the theoretical is worthless) of an AA gun is really relevent and that's only in certain engagements (ie a missile or an Kamikaze). For these engagements the logical is simple enough; as the targeting problem gets simplified the necessity to keep shooting is clear. However, keep in mind the gunner (the person aiming and firing) doesn't do the reloading. His job performance has little to do with rounds/time per clip. He must train the gun effectively and cares little about whether the gun is shooting or not in this kind of engagement.
After WW1 the ROF of a gun ranked high on the list of preferred stats. After WW2 it had fallen off a good bit. Many manufacturers had already discounted it somewhat even prior to the start of the conflict and usually regretted their decision since their buyers hadn't gotten the memo yet. The reasons ROF took a hit was that there were plenty of reports showing that the target was usually hit within the first second or two of fire for light weight, high ROF weapons. After this many factors (barrel temp, vibration, gunner concentration, target track) came into play that seriously degraded the gun's accuracy.
The swing and train rate and whether the gun was powered: This is a useful stat but only under certain conditions and most are limited to shore base batteries. These guns often suffer with having a very limited target acquisition and fire time. The ground and its many obstructions help the strikers immensely if they opt to transit the area at low altitude. As aircraft got faster and faster, this time got shorter and shorter. Swing and train rate became real issues. Ship at sea engagements don't usually afford (clouds would help) strike aircraft this luxury. Only escort ships would have much issue with it and as the data suggests, they didn't hit much when they were presented with real swing/train rate requirements. The irrelevence of swing/train rate is clearly born out if you look at the charts in the back of the document I linked. Those 5"/38's weren't worried about it because you simply can't hit aircraft very reliably if you are forced to move your barrel much.
Analyzing the joules per second of a AA gun? Not sure if that qualifies as ballastics. Novel idea I guess, but it completely negates the imperative issue of having to hit the target. It is after all the MOST important issue. And because of this the true ballistics (as normally defined, check wikipedia) of a gun is the #1 stat in gauging the accuracy and effectiveness of said gun. The higher the velocity, the heavier the round the more likely you will hit the target with an aimed shot. It is supported by every single document I've ever read regarding not only AAA but shooting in general.
Again, I seriously suggest everyone reread the linked document and think about it. Look and digest those charts towards the back. Especially the siginficance of the mission profile of the aircraft, the placement of the AA gun with reference to being on the target ship or on the escort. Even the category "Fast Carrier TF" over compared to "Other ships - Philippines" is eye opening if you grasp the notion that a "Other ship" is really a situation of an unescorted target ship.
Then remember this document pertains ONLY to the USN. The AA issues of the USN do not match up well with the AA issues of the IJN especially after 1944. For one, they held very different tactical doctrines with regard to TF ship deployment. The IJN favored maneuverability over close in AA support. Probably because they feared torpedoes above all else. Pretty logical when you consider their torps worked rather well. Yet this tactical doctrine was at the detriment to DB attacks where concentrating heavy AA around the high value unit was the best way of disrupting the DB's performance. Given the poor quality of USN torpedoes it is clear that the IJN would have been better off adopting the USN CVTF deployment doctrine.
Finally, prior to 1944 and the deployment of kamikazes the effectiveness of light AA was almost universally poor. This would have been especially true for the IJN for allied pilots were not so inclined to get ever closer to their targets in an effort to ensure a hit. Most ordnance of the day would have been released at the very limit of their effective range, giving them only a second or two of useful defensive fire. After that they became revenge guns. I think a USN skipper summed it up best when he complained about the poor morale the 20mm generated - you simply knew that when they started shooting it was time to run for cover because sailors were about to die.
BTW, in my mod the 25mm is ranked slightly above the 20mm but well below a 40mm. And it only gets ranked higher than a 20mm because there's no simulated shortage of ammo for it. While on paper the 25mm was better than the 20mm, this completely discounts how much harder it was to manufacture the 25mm round. I'm pretty sure there's a report or two (again restricted but later declassed) refering to the shortage of 25mm ammo that existed throughout 1942-45. What the Japanese did to deal with this shortage also tells you that they too knew that the first 1-2 seconds was about the only time you had a reasonable chance of hitting anything with light AA and after that it became nothing more than a revenge gun.
Gary S (USN 1320, 1985-1993)
AOCS 1985, VT10 1985-86, VT86 1986, VS41 1986-87
VS32 1987-90 (NSO/NWTO, deployed w/CV-66, CVN-71)
VS27 1990-91 (NATOPS/Safety)
SFWSLANT 1991-93 (AGM-84 All platforms, S-3 A/B systems)