Hypothetical Battle of the Java Sea...

[lwd]

http://dreadnoughtproject.org/friends/d ... 201-18.pdf
may be of some interest here. One thing to note is that the Japanese didn't seem to use a formation (at least at the beginning of the war) which maximized its air defence. Their Destroyers were often disperesed with the aim of spotting opposing aircraft rather than providing overlapping fields of fire and the curisers were often sent ahead to engage in surface combat rather than aid in fleet defence vs enemy aircraft.

[Bgile]

Yes, but the Japanese did concentrate their carriers in one task force, as opposed to USN practice of splitting them up into one TF per carrier, which made it harder to coordinate air strikes and also reduced defensive firepower.

I think the Japanese may have had the right idea early on. Given that shipboard AA wasn't terribly effective, spreading out their fleet probably gave their fighters more time to react to an incoming air attack on their carriers.

[jhoonday]

This would last until the end of February when the ABDA fleet would be virtually destroyed during the Battle of the Java Sea and the periphery naval actions.

[lwd]

Yes, but the Japanese did concentrate their carriers in one task force, as opposed to USN practice of splitting them up into one TF per carrier, which made it harder to coordinate air strikes and also reduced defensive firepower.

My impression was that US doctrine was to split CVs up into pairs rather than singles. One of the ideas being that if the enemy found one group they didn't necessarily find the entire force.

I think the Japanese may have had the right idea early on. Given that shipboard AA wasn't terribly effective, spreading out their fleet probably gave their fighters more time to react to an incoming air attack on their carriers.

Part of the problem here is that the Japanese didn't have very good radios in their planes. I remember reading in Shattered Sword that at least one of the Japanese cruisers fired its main guns to try and direct the CAP at incoming US planes. Also once radar was available lookout DDs became more of a waste and perhaps a threat as well. Again at Midway one group of US planes found the Japanese CVs by following a DD back to the fleet.

[Bgile]

Well, actually the ultimate AA defense involved a pair of radar equipped destroyers with CAP controllers and some light craft with copious amounts of AA, all stationed iirc about 50 or more miles away from the carrier TF, and four or more carriers in the same TF with a tight screen of BBs, cruisers and destroyers around them. That's what the US was doing at the end of the war, and postwar we were designing destroyers for that purpose.

[dunmunro]

Well, actually the ultimate AA defense involved a pair of radar equipped destroyers with CAP controllers and some light craft with copious amounts of AA, all stationed iirc about 50 or more miles away from the carrier TF, and four or more carriers in the same TF with a tight screen of BBs, cruisers and destroyers around them. That's what the US was doing at the end of the war, and postwar we were designing destroyers for that purpose.

I think this was a response to Special Attack tactics, and not necessarily for defense against massed attacks from CVs.

[Bgile]

It was a response to massed attack. It was required to get the CAP on to the target before it was too late to stop them, whether "them" refers to CV air strikes, Kamikazes, or jets. It was employed until the advent of good AEW. According to Friedman's "US Destroyers", it was a major consideration in postwar destroyer conversion and design of new ships. The British were forced to use this method during the Falkands war because they didn't have good AEW.

[alecsandros]

As for the actual Pearl Harbor strike times, I will read a little bit this evening and post something after that.

From Walter Lord's "Pearl Harbor": exerpt from one of Oahu's radar log:

7:02 - large contact detected, distance 137 miles
7:08 - distance 113 miles
7:15 - distance 92 miles
7:25 - distance 62 miles
7:30 - distance 47 miles
7:39 - distance 22 miles

Consequently,
Average speed (7:02-7:08) = 240mph
Average speed (7:08 - 7:15) = 180mph
Average speed (7:15 - 7:25) = 300mph
Average speed (7:25 - 7:30) = 180mph
Average speed (7:30- 7:39) = 167mph

This is not to say all the planes achieved 300mph. But it is to say that none of them closed in slower than 167mph (270km/h) at any time during the attack.

[Bgile]

It looks like the average was about 200 mph, which is what I would expect.

Nice find, by the way!

[lwd]

... From Walter Lord's "Pearl Harbor": exerpt from one of Oahu's radar log:

7:02 - large contact detected, distance 137 miles
7:08 - distance 113 miles
7:15 - distance 92 miles
7:25 - distance 62 miles
7:30 - distance 47 miles
7:39 - distance 22 miles

Consequently,
Average speed (7:02-7:08) = 240mph
Average speed (7:08 - 7:15) = 180mph
Average speed (7:15 - 7:25) = 300mph
Average speed (7:25 - 7:30) = 180mph
Average speed (7:30- 7:39) = 167mph

This is not to say all the planes achieved 300mph. But it is to say that none of them closed in slower than 167mph (270km/h) at any time during the attack.

Given the accuracy of early detection radar and the fact they weren't recording data with anymore precision the best use of this data is proably to averaage it over the entire time peirod which results in a speed of 186 mph. If they weren't coming straight in air speeds would of course be higher. The torpedo planes could have been at lower altitude and not detected also so it's rather problematic. It does however make a pretty strong case for speeds over 150/mph. Also radar often measured distances in radar miles ~ a nautical mile so if this correction has not been applied they could also be flying faster.

[dunmunro]

... From Walter Lord's "Pearl Harbor": exerpt from one of Oahu's radar log:

7:02 - large contact detected, distance 137 miles
7:08 - distance 113 miles
7:15 - distance 92 miles
7:25 - distance 62 miles
7:30 - distance 47 miles
7:39 - distance 22 miles

Consequently,
Average speed (7:02-7:08) = 240mph
Average speed (7:08 - 7:15) = 180mph
Average speed (7:15 - 7:25) = 300mph
Average speed (7:25 - 7:30) = 180mph
Average speed (7:30- 7:39) = 167mph

This is not to say all the planes achieved 300mph. But it is to say that none of them closed in slower than 167mph (270km/h) at any time during the attack.

Given the accuracy of early detection radar and the fact they weren't recording data with anymore precision the best use of this data is proably to averaage it over the entire time peirod which results in a speed of 186 mph. If they weren't coming straight in air speeds would of course be higher. The torpedo planes could have been at lower altitude and not detected also so it's rather problematic. It does however make a pretty strong case for speeds over 150/mph. Also radar often measured distances in radar miles ~ a nautical mile so if this correction has not been applied they could also be flying faster.

We know the take off time and we know the attack time. How do we account for the fact that it was nearly two hours from T/O to attack? These speeds would imply that it took almost an hour for the IJN to form up after launch, which is nonsensical.

If we assume that the IJN force went to full throttle as they approached PH, then their speeds should be increasing, not decreasing and obviously an average speed of 300mph, for example is a physical impossibility. This indicates major errors in the long range radar distance measurements, which in turn would invalidate the average speed measurements. 186mph, the average speed from the radar plot would be about equal to the full throttle speed of the slowest aircraft, the B5N2 carrying 800kg bombs. The closest range distance measurements also give the slowest speeds.

[Bgile]

The smaller time segments would likely be in error because the radar wasn't that accurate, but I would think that if we take the total time and distance it should be in the ballpark. With regard to actual times, maybe the time used by the radar operator was incorrect ... I can't explain it. But what we do have is the Japanese air strike plotted from one point to another, with seemingly a good idea of about how fast it was going.

I also think the B5N cruised at about 10,000 feet. Isn't that correct from Midway attack records? I was thinking the Swordfish normally cruised at about 5,000 feet. Is that true, or do I have the wrong impression?

[Bgile]

We know the take off time and we know the attack time. How do we account for the fact that it was nearly two hours from T/O to attack? These speeds would imply that it took almost an hour for the IJN to form up after launch, which is nonsensical.

The torpedo planes attacked from the South East and had the longest distance to travel prior to their attack run. They made a big loop to the east of PH before turning NW for their run in to battleship row.

[tommy303]

Japanese tests in August of 1941 in Kagoshima Bay showed that the type 91 Mod 2 could be dropped by the B5N Kate at speeds as high as 160 knots )184 mph, and began to develop suitable tactics for using those speeds against enemy ships. These 'high' speed attacks were later employed at Pearl Harbour since it was found the torpedoes would not plunge too deep even at such speeds. This agrees pretty much with British and American crews recounting Japaanese torpedo bombers executing attacks at much greater speeds than had been practiced for in peacetime.

[dunmunro]

Japanese tests in August of 1941 in Kagoshima Bay showed that the type 91 Mod 2 could be dropped by the B5N Kate at speeds as high as 160 knots )184 mph, and began to develop suitable tactics for using those speeds against enemy ships. These 'high' speed attacks were later employed at Pearl Harbour since it was found the torpedoes would not plunge too deep even at such speeds. This agrees pretty much with British and American crews recounting Japaanese torpedo bombers executing attacks at much greater speeds than had been practiced for in peacetime.

The IJN would approach the target at 10K+ altitude then use a shallow dive to increase speed, while within range of AA, so speeds around 200knots are possible in this phase, with a small deceleration before the actual drop. Top sustained speed at sea level with a torpedo was probably around 200mph, for the B5N2.