The invasion of Oahu, December 1941.

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robdab
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blockships & elephants ...

Post by robdab » 22 May 2007 20:42

Glenn,
wrt a blockship, as you know, there were 5 Japanese minisubs at hand (carrying 2 torpedoes each) that morning which could have been ordered instead to deal with USS Ward. (And for that matter another 5 full sized mother-subs, nearby). On slow patrol she would have been 'easy meat' for a single torpedo hit at about 0730, as a blockship approached.

As for the "exclusion zone" that you mentioned, I was ONLY aware of it refering to unidentified submarines ? If you have a source that indicates that there WAS also a surface vessel exclusion zone in operation (and its size/orientation since such would have been published in commercial shipping journals of the day) on Dec.7'41, than please provide same for my ongoing education.Certainly, if such a surface vessel exclusion zone existed and IF any of the US defenders were awake enough to report transgression into same, then, with the warning time thus provided, the US CA delivered consequences would have been truely dire for any trespasser. However, at this time I do NOT believe that to have been the historical case.

The amount of bandwidth needed will likely be determined by this information although depending on the details, it MIGHT also have been possible for a highspeed blockship approaching thru darkness/mist to transit most of a surface exclusion zone before causing a US alarm to be raised. As is often said, "timing is everything".

It is known that the PH ship channel anti-submarine nets (actually only 1918 vintage thin anti-torpedo nets) were opened daily from approimately 0500 to 0900 to allow the passage of two minesweepers, a garbage barge and general cargo shipping in and out of that busy military port. Easily reported to Japan by her Honolulu consular staff, if asked, and perfect for a blockship approaching at 0730 +/-. Certainly, a blockship with sufficient mass/speed to push thru/over a closed harbor net would have had to have been selected for this mission but I suspect that such an effort would not have been needed. Any (20' high) minisub still carrying torpedoes could then easily slip into PH as they did historically thru an open net or UNDER the 45' deep net which was hung over a 72' deep channel. Or, wait in ambush ouside for any US targets of opportunity.

IYR there were only two alert or examination batteries that shared the responsibility for security over the Pearl Harbor ship channel. Battery Hawkins (2x3") and Battery Jackson (2x6") both located in Fort Kamehameha on the east side of the Pearl Harbor ship channel shared the duty but I am NOT sure about which had that responsibility on the morning of Dec.7'41. I do believe that ONLY one of these two batteries would have been ready to fire almost instantly (at least, once warned) on an approaching blockship. Yes, there WERE numerous other manned Coastal Artillery installations within range of the PH ship channel that Sunday morning but none other had its gunners, "at their sights", nor ready ammunition to hand. Yes, all WOULD have fired eventually but since a blockship is SUPPOSED to sink anyway, it would likey have been too late to prevent a channel blockage. Certainly, a few 3" or 6" hits would not have knocked a blockship off of her course.

Especially a blockship that had been shipyard modified with numerous valved seacocks thru her bottoms designed to speed her settling and additional, stronger anchors/chains to hold her on her blocking position, while sinking.



Chris,

should the Japanese invasion go well it would be a fairly quick operation to have divers enter the shallow water sunken hull, close the seacock valves and with pumps, refloat the blockship. A matter of days, not weeks or months.

Wrt your comments about trying to capture Oahu's fuel, I think it unlikely in the extreme. With all of the tanks vulnerable to .50 cal and a flare gun or a US defender who knows how to open a valve and light a match, they ARE going to burn if the defence is going badly. Much better for the Japanese to light them off after a blockship is in place and wait for the 250,000,000 gallons of flaming fuel to incinerate most of the now trapped, US Pacific Fleet. That way a much larger portion of the Kido Butai's airstrikes could be devoted to gaining complete air superiority over Hawaii instead of sinking the USN warships inside PH. Any survivors couldn't be leaving the harbor anyway and would be easily dealt with over the following few days by aircraft or IJN bombardment.

Since I am a great believer in the phrase, "no guts, no glory", I would suggest that the only way to have any chance at all of capturing a fuel tank farm or two (of the 4 present) would be to drop IJA and IJN paratroops on Oahu as was attempted a few short months later on at least two NEI refineries. With 80% casualties resulting. Historically, those paratroops were not well enough trained by Dec.7'41 to have been used then but in an alternate history one can suggest that by starting training earlier, they might indeed have been ready ? If presented with that arguement however, I would counter with the question of where would all of the aircraft needed to drop a large force of paratroops, have come from ? The Japanese "Nell" was the only twin engined land based bomber that DID have the one-way range to fly to Oahu from the Marshall Islands but could carry only 8 paratroops per plane at that distance. Thus, over 120 (additional planes to carry heavy weapons) destroyed land based bombers (and some of the very hard to replace pilots) to carry one single 800 man battalion to Oahu, with no guarantees that some of the planes might not miss the island all together on a long overnight flight. And no guarantees that they would parachute onto the right locations, survive any AA fire or even fight effectively once there. Possible but not at all likely IMO.

Wrt your comments about a large white elephant in a small room, you seem to be forgetting about real history. Glenn is basically just shifting the Phillipines invasion to Oahu, with more warships. If the US didn't "twig" to the real invasion of the Phillipines, even with the 8 hours of warning given by the real Pearl Harbor air raids, what makes you think that they could have figured out in this alternative history that Oahu was about to be invaded ? The Japanese wouldn't be sending a telegram to the Phillipines saying, "You're safe, this time", now would they ? The US still had far too few codebreakers and would still be concentrating those few on diplomatic messages, not on naval codes. And the US defenders of Oahu were still NOT doing the long range air searches needed to prevent a sneak attack on Oahu. A large white elephant in a room is still NOT seen unless someone opens a door and actually LOOKS inside.

I would agree with you about Glenn's use of the entire Combined Fleet at Oahu though. I think it unlikely that the IJN would leave the Home Islands completely 100% undefended, even though their desire would be to have every Japanese battleship (9 ?)present for the final, great "Decisive Battle" just off of Oahu, if a blockship/firestorm didn't do the trick.

Perhaps Glenn could adjust his naval bombardment needs so as to allow a reserve force of 2-3 fast battleships etc., to be positioned near say, Saipan so as to be able to respond to unfolding events to the east, to the south or back near Japan ?

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Post by glenn239 » 22 May 2007 22:58

Don't mean to detract from your work Glen, and while it looks good in some operational/tactical aspects and the details are excellent, it fails on the most basic element to all successful military operations , the element of suprise.
The conclusions contain information pertaining to the USN's ability to track IJN warships prior to December 7th and the estimate that this will lead to a premature detection of the force. (I rate the odds as low). With respect to invasion convoys, the major ones are in Japan at the start of the scenario (ie, they haven't sailed yet). Another is at the Marshall Islands.
Why bomb the oil tanks( and some other really useful things- navy yard, etc.) if you plan on quickly taking over Oahu? Seems like ALOT of oil that your (insert appropriate WWII derisive slang terms) could dam sure use later. In many ops the Japanese counted on seizing even just food to support their ops.
By destroying Pearl Harbor's oil, the IJN forces the USN to vacate Hawaiian waters, which in turn assures that Hawaii and Maui will fall. If, on the other hand, the oil is not dealt with, then this adds an additional complication (USN fleet elements might attack an invasion convoy), while removing entirely the chance that the effects of the tanks' destruction will take out the navy yard, Cinpac HQ and the submarine base.
On slow patrol she would have been 'easy meat' for a single torpedo hit at about 0730, as a blockship approached.
What military op in WW2 can you recollect where a submarine had to torpedo a destroyer (or any ship) at a specific moment in time?
As for the "exclusion zone" that you mentioned, I was ONLY aware of it refering to unidentified submarines ? If you have a source that indicates that there WAS also a surface vessel exclusion zone in operation (and its size/orientation since such would have been published in commercial shipping journals of the day) on Dec.7'41, than please provide same for my ongoing education.
I'm unaware that either the Panama or Pearl exclusion zones were pertinent only to one particular type of ship. If so, this would be an incredible oversight since Kimmel knew a single Maru might block the channel.
it MIGHT also have been possible for a highspeed blockship approaching thru darkness/mist to transit most of a surface exclusion zone before causing a US alarm to be raised. As is often said, "timing is everything".
Right, but the whole thing starts sounding more like Guns of Naverone or The Eagle Has Landed.
Wrt your comments about a large white elephant in a small room, you seem to be forgetting about real history. Glenn is basically just shifting the Phillipines invasion to Oahu, with more warships.
The state of the American art in tracking IJN warships during December 1941 was largely checkmated by IJN countermeasures. These included encoding ship call signs (I think), changing the codes to a newer variant, strict radio silence, and false signals generated in Japan for various ships. With respect to radio silence, the Congressional Hearings established that silent Japanese ships and divisions were always assumed to be in port. It was not unusual for the USN to lose track of large chunks of the Japanese fleet for weeks at a time.

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Post by ChristopherPerrien » 23 May 2007 00:19

x2 post
Last edited by ChristopherPerrien on 23 May 2007 00:30, edited 1 time in total.

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Post by ChristopherPerrien » 23 May 2007 00:19

I won't argue with either of you, however I think you both need to read up more on the state of US intelligence, Sigint , Comint , and Humint at the time. Neither the suprise attack on Pearl Harbor nor MacArthur's incompetence is even a remote excuse to think this elephant would work/fly/etc.. War-game it all you want , but in OTL this would NEVER have worked.

Chris

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Post by Carl Schwamberger » 23 May 2007 01:28

A truly impressive analysis. So far removed from the usuall proposals of a Oahu invasion by Japan that there is no comparison.

The only point (& a minor one) I have any ability to critique today concerns the artillery of the ground forces post landing on Oahu. Refering in part to:

"Oahu garrison firepower guesstimate by shell type
(HE types only)

Type...........Qty..........25lbr..........Total
240mm......3,000.........6.75.........20,250
8"..............3,600.........3.08.........11,088
155mm.....139,355.......2.9.........404,129
75mm.......415,318.......0.5.........207,659
81mm........15,395........0.5...........7,698
Total.........................................650,824 25lbr equivalents"

ect...

1. The website your drew the information from concerning "25lbr equivalents" is the best for refrencing British artillery, but I suspect it is less usefull for other nations. The '25lbr equivalent' itself is influenced by some Brit assumptions about artillery and is not a proven unit of measurement. Unfortunatlly the best source I am familar with is not available and the other methods of measurement individually are less usefull than the '25lbr equivalent'. Still it is a minor thing.

2. The comparison of shell weight is a partial & inadaquate measurement. Differences in technique & tactical doctrine are critical. These seem to have been large & significant between the US Army and IJA artillery in 1941-42. I cant & wont at this point go into which would have been at the advantage. If and when you delve into this seldom trob pathway contact me & I'll dig up a few more sources for you and discuss it further.

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Blockship continued ...

Post by robdab » 23 May 2007 06:15

Glenn,
Your comment of, "What military op in WW2 can you recollect where a submarine had to torpedo a destroyer (or any ship) at a specific moment in time ?" is certainly valid but please consider the context of the situation. When not rushing about chasing down submarine contacts reported by the USS Antares, USS Ward traced and retraced a regular 1 mile by two mile rectangular patrol "box". Using pre-war intell. the five Japanese minisubs could easily have positioned themselves such that Ward was NEVER more than 1/2 a nm from at least one of them and for the vast majority of the time, within 1,000 yds of two of them. Without even considering the 5 Japanese mother-ship submarines also present. While this positioning might not guarantee a torpedo hit at exactly 0730, the timing would be "close enough", I'm sure.

Another tactic which might have been tried would have been to have the minisubs clustered around the blockship. Since the American of the day were unaware that Japanese minisubs even existed, Ward was unlikely to have taken anti-submarine precautions while intercepting a suspicious merchant vessel in the shallow waters of the Pearl Harbor ship channel approaches.

The other comment of yours that I noticed was, "I'm unaware that either the Panama or Pearl exclusion zones were pertinent only to one particular type of ship. If so, this would be an incredible oversight since Kimmel knew a single Maru might block the channel."

Would you really be even remotely surprised if the US defenders of Oahu were shown to have made yet ANOTHER incredible oversight on Dec.7'41 ? Do you really need me to once again recite the unbelievable list of screw-ups that allowed the success of Japan's historical Pearl Harbor raid ? The list is nearly endless. No long range air patrol, no functioning fighter direction centre, radar reports of inbound airstrikes ignored, USN attacks on Japanese submarines not reported to the US Army, ammunition locked up miles from the guns that needed it, no obsevers posted in Oahu's 100+ coastal artillery spotting stations, airplanes lined up wing-tip to wing-tip on Oahu's runways without fuel, machine guns or ammunition loaded. Need I go on ?

I have found only Kimmel's letter at http://www.ibiblio.org/pha/pha/hart/xha-004.html which deals with air and submarine attacks and http://www.ibiblio.org/pha/pha/hart/xha-005.html which defines the Pearl Harbor defensive zone boundaries. Apparently Kimmel wrote a letter on Nov.27'41 authorizing immediate attacks on submerged submarines operating in certain areas near to the Pearl Harbor ship channel but I have yet to find a copy. I would expect any such order to also mention foreign warships encountered in any such restricted areas but I have NO basis on which to believe that civilian merchant vesels would be so targeted in a time of peace.

I seems that neither of us can yet "prove" our point of view ! Happy hunting !

Can you refer me to any sources reguarding the Panama Exclusion Zone that you mentioned ?

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Post by glenn239 » 24 May 2007 01:22

I won't argue with either of you, however I think you both need to read up more on the state of US intelligence, Sigint , Comint , and Humint at the time.
Essentially, you are proposing that somewhere between the force structure of 20 combat vessels which ambushed Oahu on December 7th 1941 and the force structure of about 75 combat vessels committed here, there was a watershed at which the USN 'must' detect what the IJN was up to. Perhaps. But what I concluded is that in December 1941 the USN was less certain of detecting a move on Hawaii in force than at any other point during the entire war. Which, irrespective of the chance of failure, seems to suggest that December 1941 was the vulnerable moment because it represented the only period when IJN countermeasures were on par with USN capabilities in this regard.

Once the Japanese expanded overseas in 1942, much of their fleet tended to be based at, or transiting to and from, places all over the Pacific. This allowed their movements to be tracked more easily as units switched between various theatres and commands for this op or that op, places only connected by radio. When in Japan, this could be done by other means such as the telephone.

In this scenario Zuiho and Hosho and some other lighter ships might be fixed by USN signet as being in the Marshalls because thier movements fits that pattern, regardless of the fact that JN25B wasn't yet cracked. But that's small potatoes, and could act as a distraction to the main blow coming straight out of the blue across the North Pacific.

With respect to a blown cover, IJN traffic analysis would see Hawaiian radio volume go through the roof in only a few hours. The fall-back operation, specified but not detailed to any great degree, would see 7th I.D. (the Kauai Invasion Unit) take Midway while the Main Body and Strike Force awaited a naval battle nearby with Kimmel. If this did not happen, then Strike Force and other elements (Hawaii, Johnston and Maui Invasion units) are used to take Johnston, Palmyra, Samoa and Rabaul before the operation winds down; again looking to see if Kimmel would sortie. It can be imagined that Kimmel, not being aware of the true power of Yamaguchi's Strike Force, would come out.
The website your drew the information from concerning "25lbr equivalents" is the best for refrencing British artillery, but I suspect it is less usefull for other nations. The '25lbr equivalent' itself is influenced by some Brit assumptions about artillery and is not a proven unit of measurement.
Agreed completely. I fished around for a method on how to look at artillery and the like for quite some time. The problem is that I couldn't find anything out there that really did what I was looking to do. I expected, literally, to find some sort of pamphlet published by different militaries from the war listing targets and denoting how many of what type of shells and bombs were required for what effect. That is to say, you look up a target type ("airbase"), punch in the size ("200,000 square yards") and the desired effect, and out pops the number of widgets you need to accomplish the goal. I began to suspect that this might never have been done, which seems incredible.

On the measurements themselves, if I ever revisted this monster these would be amongst the first things I'd like to improve. But what is there I think isn't bad at scaling the different firepower inputs, and the raw horsepower available to each side. How much of the Navy Yard could Yamato really pummel with 450 18.1" shells? I doubt it's what I concluded, but I also think that the answer I provided would be a sufficient basis for planning the operation, because it's probably in the ballpark. If you run across methods to improve on this, let me know.
While this positioning might not guarantee a torpedo hit at exactly 0730, the timing would be "close enough", I'm sure.
Whereas I'm not. What if Ward spots a mini-sub prematurely and then rushes around for the next two hours at 28kt?
Need I go on?
Yes. Whether or not surface ships were barred from the restricted zone will have had nothing to do with Army aircraft being lined up wingtip to wingtip. You have to find the reference that says the coastal guns and patrolling ships would not have blasted the blockship out of the water the moment it crossed a certain point. If you can do this, then you've established a basis by which you can proceed on your scenario. Though, I would add, if I were you I'd investigate whether you could cough up an American or British flagged ship from somewhere, rather than a Japanese one.
Can you refer me to any sources reguarding the Panama Exclusion Zone that you mentioned ?
None, I'm afraid. I seem to recall that all ships were stopped and boarded outside it as a matter of routine

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Post by Carl Schwamberger » 25 May 2007 00:55

glenn239 wrote:

None, I'm afraid. I seem to recall that all ships were stopped and boarded outside it as a matter of routine
Transiting the Panama Cannal has always required the ship be navigated thru by a experinced pilot specializing in the Cannal. The ship also gets a safety or hazards check. The last thing anyone wants is a engine malfunction or the cargo catching fire while in one the channels or locks. And dont think the concern about ship fire is spurious. It happened often in those days, and is still a significant problem with both military & merchant vessels.

http://www.local1259iaff.org/disaster.html

From 1940 the US military also took a close look at the ships transiting the cannal from the standpoint of sabotage. These inspections were not perfect,neither were the other safeguards, but in late 1941 it would have required a really imaganitive plan and no small luck to block the Cannal.

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Blockship yet again ...

Post by robdab » 25 May 2007 02:56

Glenn, you wrote:
"Whereas I'm not. What if Ward spots a mini-sub prematurely and then rushes around for the next two hours at 28kt?"

IIRC it was first a US minesweeper and later USS Antares that spotted a supposed following submarine, in the dark, and reported it to USS Ward. Ward was by no means sure that it was a real contact or just a lookout's nightime fantasy.Would any US peacetime DD skippers expect FIVE (5) submarines to be close at hand and actually STALKING him, especially when it was NOT at all known that Japan had developed minisubs, effective in much shallower coastal waters than would have been available to their full-sized mother-ships ? I believe that the standard US anti-submarine tactic of the day was to quietly sit on top of a submarine's last reported position (since it was difficult for the submarine to torpedo you while you were parked almost on top of him) and then listen via hydrophones (or better still, use active sonar if so equipped as only very few US DDs of the day at PH were) to try to locate it precisely for a depthcharge drop. Hard for Ward to use her sonar at all when charging around at 28kts and we know via Prange that she DID use her sonar in an unsuccessful atempt to find the minisub, so she wouldn't likely be doing 28kts in my scenario, either. And if looking for a (phantom ?) sub, how could Ward have been stopping, boarding and searching a lost merchant ship that had been found to be inside this mystery exclusion zone around the PH ship channel ? If so, she then becomes a STATIONARY target for 5 minisubs instead of JUST 4.

IIRC Ward was also drawn out of her patrol pattern to check a large sampan sighted near to her action with the minisub. I could easily propose some similar type of distraction designed to get her temporarily away from the ship channel entrance. One patrol destroyer can't do everything and be everywhere at once, now can it ?

So, I think that we'd see a chain of events similar to what happened in reality that day. USS Ward sinks a Japanese minisub, is sunk in turn by one of the other 4 Japanese minisubs close at hand, so the action ISN'T reported up the unresponsive US chain of command, PH ISN'T alerted in time (only about 25 minutes to go until the Kido Butai's airstrike comes in at 0755) to react effectively and the Japanese attack goes in yet again with similar devastating results. As a blockship picks its way into the Pearl Harbor ship channel. Under direct fire from 2x3" and/or 2x6" to be sure but are these 2/4 guns likely to sink this large & determined high speed vessel BEFORE she enters the ship channel ?? I doubt it.

"You have to find the reference that says the coastal guns and patrolling ships would not have blasted the blockship out of the water the moment it crossed a certain point. If you can do this, then you've established a basis by which you can proceed on your scenario."

And why is the onus on me to find a source that says this ? YOU are the one CLAIMING (only from memory apparently) that the exclusion zone included surface vessels but I have seen NO source at all from you in support of anything of the sort. I HAVE provided one source that mentions ONLY submarine, aircraft and mine attacks. I have supported my point, it remains to you to refute it with sources other than your opinion.

Having stated that, on page #96 of Prange's book "Dec.7, 1941" the author mentions that normal procedure when the USN found a sampan in the defensive sea zone was to ask the Coast Guard to send out a cutter to escort it back into Honolulu Harbor. Hardly the firestorm of defensive US Coastal Artillery fire that you seem to feel would have been the instant reaction to any such transgression. It WAS still peacetime, don't forget.

" Though, I would add, if I were you I'd investigate whether you could cough up an American or British flagged ship from somewhere, rather than a Japanese one."

I'm already well ahead of you, one step better in fact, on this one.

During WW1 many nations disguised/modified their merchant ships for commerce raiding purposes. In the case of Oahu at 0830 on Dec.7'41, the Dutch 10,000 ton fast cargoliner 'Jagersfontain' arrived off of the entrance to the PH ship channel carrying a load of beer for the US navy on her regular trans-Pacific run from San Francisco. Due to the surprise air attack she diverted to Honolulu Harbor, entering at about 0900. She became the first Allied ship of the Pacific War to aid the US when her bridge wing AA guns opened up on Japanese aircraft flying overhead. No surprise really when you consider that she was ALSO carrying a load of dynamite, in addition to pasengers bound for the Dutch East Indies, at the time.

Since hers was a regularly scheduled run and Japanese agents at San Francisco could have easily reported her departure, I think it relatively a simple thing for a similarly configured Japanese blockship to have been slightly re-configured by carpenters and repainted/reflagged while at sea, to more closely resemble her. An earlier 0700 arrival time, a bold approach and the horror of accidentally firing at the expected "beer ship" would have nearly guaranteed her passage up the Pearl Harbor ship channel, in complete safety. LOL.

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Post by Carl Schwamberger » 25 May 2007 03:10

This block ship for Pearl come in part to weather a harbor pilot was needed and where he would have habitually come aboard. If one was required then a block ship attempting to 'rush' the channel is going to attract instant attention since no legitimate skipper is going to risk losing his license and or grounding his ship by charging in without picking up the pilot.

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Blockship ongoing ...

Post by robdab » 25 May 2007 05:37

Carl,
I'm not sure of the point(s) that you are trying to make with your last post ? Of course a blockship IS going to attract LOTS of hostile attention. At least, just as soon as the PEACETIME defenders REALIZE that it might be a blockship, anyway. Thats why, in times of war, most protected ports had examination batteries watching for just such a "rush", manned and ready to shoot, 24/7, AND naval patrols at some distance off of the harbor mouth. No nation wanted that kind of nasty surprise OR wanted to shoot up a ship just making a mistake due to language problems etc.

In the case of Pearl Harbor on Dec.7'41, the questions to be discussed are 1.) when/where will it attract that first attention 2.) who's attention will be first attracted (USS Ward or the two examiniation batteries ?) 3.) Can Ward be disabled before seriously hurting that blockship 4.) how long will it take for a warning to spread so that the MUCH larger coastal artillery batteries in range, can begin to fire at the blockship 5.) was interception/sinking by USAAF or USN aircraft possible given the warning times available and finally 6.) was it possible for any other USN vessel(s) to leave Pearl and intercept/sink the blockship BEFORE she reached a position which could block the ship channel ?

The chances of blockship success will greatly change depending on whether she is detected as a potential threat to PH at some 10 miles out or 1/2 mile out. Timing IS everything in this case. If she gets to the pilot pick-up point without being reported as hostile then she is ALREADY past both of the examination batteries so rushing the historically open net won't be a big problem. If detected 10 miles out then some 16" CA guns will ruin her day.

We know that the USN aux.cargoship USS Antares waited for 35 minutes just 1/2 mile outside the PH nets for a tug to bring a Pearl Harbor pilot out to her. We also know that neither of the two minesweepers that returned to Pearl Harbor just after 0458 waited to pick-up a pilot at all. I can only guess it was a case of "familiarity breeds contempt" ?

Also Carl,
Its probably just me but I couldn't get the Panama link that you posted to open for me.

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Post by glenn239 » 26 May 2007 00:57

Rob, can you cite an example where a Japanese mini-sub ever torpedoed a vessel that was underway at any point during the war?

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Re: Blockship ongoing ...

Post by Carl Schwamberger » 28 May 2007 01:26

robdab wrote:Carl,
I'm not sure of the point(s) that you are trying to make with your last post ? Of course a blockship IS going to attract LOTS of hostile attention. At least, just as soon as the PEACETIME defenders REALIZE that it might be a blockship, anyway. Thats why, in times of war, most protected ports had examination batteries watching for just such a "rush", manned and ready to shoot, 24/7, AND naval patrols at some distance off of the harbor mouth. No nation wanted that kind of nasty surprise OR wanted to shoot up a ship just making a mistake due to language problems etc.

In the case of Pearl Harbor on Dec.7'41, the questions to be discussed are 1.) when/where will it attract that first attention 2.) who's attention will be first attracted (USS Ward or the two examiniation batteries ?) 3.) Can Ward be disabled before seriously hurting that blockship 4.) how long will it take for a warning to spread so that the MUCH larger coastal artillery batteries in range, can begin to fire at the blockship 5.) was interception/sinking by USAAF or USN aircraft possible given the warning times available and finally 6.) was it possible for any other USN vessel(s) to leave Pearl and intercept/sink the blockship BEFORE she reached a position which could block the ship channel ?

The chances of blockship success will greatly change depending on whether she is detected as a potential threat to PH at some 10 miles out or 1/2 mile out. Timing IS everything in this case. If she gets to the pilot pick-up point without being reported as hostile then she is ALREADY past both of the examination batteries so rushing the historically open net won't be a big problem. If detected 10 miles out then some 16" CA guns will ruin her day.

We know that the USN aux.cargoship USS Antares waited for 35 minutes just 1/2 mile outside the PH nets for a tug to bring a Pearl Harbor pilot out to her. We also know that neither of the two minesweepers that returned to Pearl Harbor just after 0458 waited to pick-up a pilot at all. I can only guess it was a case of "familiarity breeds contempt" ?

Also Carl,
Its probably just me but I couldn't get the Panama link that you posted to open for me.
I think to answer this question a exam of the procedures of the USN for ships entering PH needs to be examained in far more depth. Since PH was not a civilian port, had few comercial ships entering it, and the schedule of those destined there was fairly known anything approaching PH will attract attention. And, the concern for sabatoge was paramount in 1941. So we woud need to know exactly what the standing orders were, the procedures, and the actual practices for late 1941.

Harbor navigation of a USN ships homeport was susposed to be part of the officers qualification for standing bridge watch and taking the con of a ship. This was particularly important for the smaller vessels which did the patroling. Its the same for small coastal freighters and harbor service vessels like tug boats. Which bring up a question of navigation of the harbor entry. I dont know how difficult PH is. In the dark with some strong currents,fast tides, and the usual pecularities its more likely a blockship would be grounded before entering the harbor. To prevent this the Japanese would need to locate someone with enough experince to navigate the channel entry at high speed at night.

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Pearl Harbor blockship ...

Post by robdab » 28 May 2007 20:54

Glenn,
No, I can't site any reference to a Japanese minisub actualy torpedoeing a moving USN warship BUT there certainly WAS an ALMOST and that at Pearl Harbor. Just as the light cruiser, USS St. Louis exited the PH ship channel, two Japanese 18" minisub torpedoes were fired at her but detonated prematurely after hitting coral heads. The web site http://www.ew.com/ew/article/0,,256589,00.html records the eyewitness report of a St. Louis crewman who felt that his ship was going to be "taken out" by that salvo, at least until the coral interveined.

Imagine the effect had the minisub that DID pentrate Pearl Harbor (rammed and sunk by DD USS Monahaghn after firing two torpedoes that missed) INSTEAD stopped to lurk at the West Loch branch of the ship channel. She could have easily put two 18" torpedoes into the starboard side of St.Loius BEFORE that 10,000+ light cruiser had worked up to 22 kts and created a huge US blockship without the need for a Japanese one. Of course, any US skipper would have tried mightily (as did the skipper of the USS Nevada) to beach his stricken ship anywhere she wouldn't block the ship channel. A Japanese blockship making for the same area of the channel would have guaranteed "a cork in the bottle" closure although such a double seal would have been very, very difficult to co-ordinate..

Had a torpedo attack(s) been made on USS Ward while she was doing her historical 3-4 knot anti-minisub sonar search some 3-4 miles outside of the PH ship channel entrance, in the 1,200' depths found there, then NO coral heads could have been present to "soak up" any torpedoes. And with 5 minisubs to provide the torpedoes. For that matter, ANY or ALL of the 5 Japanee mothership submarines would have had NO trouble at all in using 1,200' deep water to approach close enough for a good torpedio solution on USS WARD since her patrol box pattern was probably well known to the Japanese. In spite of the Nov.27'41 "War Warning" the proceedutres of the US defenders of Oahu were still in the form of "bad habits" and not changed regularly. Just at a time when "predictable" was about to change meaning to "dangerous".

We also know that St.Louis was doing some 22kts as she exited from the PH ship channel where normal exit speeds were limited to 8 kts by the USN. This speed difference may have thrown off the torpedo firing calculations of whichever Japanese minisub skipper fired at her but would not have been a factor if firing at the USS WARD while she was on sonar search (or even her regular 8 knot patrol box) speed.

Apparently the Japanese had sent three naval experts to Oahu in November '41 (aboard one of the three repatriation liners sent thru Honolulu) to familiarize themselves with all naval aspects of the planned minisub mission into Pearl Harbor. As a result US offshore patrol box locations & proceedures/speeds were probably well known to the Japanese minisub skippers as would have been US proceedures/habits/timings for PH entry thru the anti-submarine nets.

Carl,
I agree with most (but not all) of your post BUT where do you suggest that I find all of this almost 65 year old data ? This is the great frustration of 'alternative history', where/how to find the facts that you need to "prove" your theory ? Certainly regularly scheduled shipping would be well known, which is why I suggested using the "beer ship" coverplan.

I have a 1938 navigation chart which shows a "straight-in thru two buoys" approach to the Pearl Harbor ship channel (antisub nets weren't present in 1938 and all of the coral had been dredged/blasted out of the way several decades previously) and one of Glenn's first 20 postings on this thread indicates an Oahu tidal range of only about 1.5' maximum so I don't see either of those as a problem.

No strong currents indicated on the chart either and no major rivers draining out thru PH to generate any strong river currents/sandbars/mudflats in the ship channel.

Japanese consulate personnel and the November visit of her three naval experts would have provide any/all of the surface information needed wrt ship channel navigation such as significant landmarks + way-points on shore. As mentioned previously the 10,000+ ton light cruiser, USS St. Loius, exited doing 22kts instead of the usual 8 kts so I can't imagine there being ANY unusual or dangerous obstacles to navigation within that ship channel. Can you ?

Keep in mind that it was NOT at all desireable for a blockship to traverse the entire length of the ship channel and enter Pearl Harbor itself. The best location to acheive before sinking herself would be the point where the dredged depth of the ship channel changed from the 75' depth at the entrance nets to the 40' dredged depth maintained inside the entire area of Pearl Harbor (and no, I don't know exactly where that point was). An old fashioned "leadline" would do the trick if such depth data coukldn't be found by the Japanese in any other fashion. A sharp turn to port or starboard would place the blockship squarely ACROSS the 100yard width of the dredged ship channel with little (dredged deep water) room to spare at either end. Fore and aft anchoring would hold her in place while seacocks were opened and she settled to the bottom. Scuttling charges could certainly have been used to blow her bottoms out BUT this would NOT be desireable in terms of quickly re-opening the ship channel after Oahu fell to the Japanese.

No pilot needed, just hold to the right side of the buoyed channel until dropping the stern anchors, just before the final sharp turn to port where the bow anchors are let go.

robdab
Member
Posts: 778
Joined: 30 Mar 2007 15:45
Location: Canada

Pearl Harbor blockship ...

Post by robdab » 28 May 2007 20:55

Glenn,
No, I can't site any reference to a Japanese minisub actualy torpedoeing a moving USN warship BUT there certainly WAS an ALMOST and that at Pearl Harbor. Just as the light cruiser, USS St. Louis exited the PH ship channel, two Japanese 18" minisub torpedoes were fired at her but detonated prematurely after hitting coral heads. The web site http://www.ew.com/ew/article/0,,256589,00.html records the eyewitness report of a St. Louis crewman who felt that his ship was going to be "taken out" by that salvo, at least until the coral interveined.

Imagine the effect had the minisub that DID pentrate Pearl Harbor (rammed and sunk by DD USS Monahaghn after firing two torpedoes that missed) INSTEAD stopped to lurk at the West Loch branch of the ship channel. She could have easily put two 18" torpedoes into the starboard side of St.Loius BEFORE that 10,000+ light cruiser had worked up to 22 kts and created a huge US blockship without the need for a Japanese one. Of course, any US skipper would have tried mightily (as did the skipper of the USS Nevada) to beach his stricken ship anywhere she wouldn't block the ship channel. A Japanese blockship making for the same area of the channel would have guaranteed "a cork in the bottle" closure although such a double seal would have been very, very difficult to co-ordinate..

Had a torpedo attack(s) been made on USS Ward while she was doing her historical 3-4 knot anti-minisub sonar search some 3-4 miles outside of the PH ship channel entrance, in the 1,200' depths found there, then NO coral heads could have been present to "soak up" any torpedoes. And with 5 minisubs to provide the torpedoes. For that matter, ANY or ALL of the 5 Japanee mothership submarines would have had NO trouble at all in using 1,200' deep water to approach close enough for a good torpedio solution on USS WARD since her patrol box pattern was probably well known to the Japanese. In spite of the Nov.27'41 "War Warning" the proceedutres of the US defenders of Oahu were still in the form of "bad habits" and not changed regularly. Just at a time when "predictable" was about to change meaning to "dangerous".

We also know that St.Louis was doing some 22kts as she exited from the PH ship channel where normal exit speeds were limited to 8 kts by the USN. This speed difference may have thrown off the torpedo firing calculations of whichever Japanese minisub skipper fired at her but would not have been a factor if firing at the USS WARD while she was on sonar search (or even her regular 8 knot patrol box) speed.

Apparently the Japanese had sent three naval experts to Oahu in November '41 (aboard one of the three repatriation liners sent thru Honolulu) to familiarize themselves with all naval aspects of the planned minisub mission into Pearl Harbor. As a result US offshore patrol box locations & proceedures/speeds were probably well known to the Japanese minisub skippers as would have been US proceedures/habits/timings for PH entry thru the anti-submarine nets.

Carl,
I agree with most (but not all) of your post BUT where do you suggest that I find all of this almost 65 year old data ? This is the great frustration of 'alternative history', where/how to find the facts that you need to "prove" your theory ? Certainly regularly scheduled shipping would be well known, which is why I suggested using the "beer ship" coverplan.

I have a 1938 navigation chart which shows a "straight-in thru two buoys" approach to the Pearl Harbor ship channel (antisub nets weren't present in 1938 and all of the coral had been dredged/blasted out of the way several decades previously) and one of Glenn's first 20 postings on this thread indicates an Oahu tidal range of only about 1.5' maximum so I don't see either of those as a problem.

No strong currents indicated on the chart either and no major rivers draining out thru PH to generate any strong river currents/sandbars/mudflats in the ship channel.

Japanese consulate personnel and the November visit of her three naval experts would have provide any/all of the surface information needed wrt ship channel navigation such as significant landmarks + way-points on shore. As mentioned previously the 10,000+ ton light cruiser, USS St. Loius, exited doing 22kts instead of the usual 8 kts so I can't imagine there being ANY unusual or dangerous obstacles to navigation within that ship channel. Can you ?

Keep in mind that it was NOT at all desireable for a blockship to traverse the entire length of the ship channel and enter Pearl Harbor itself. The best location to acheive before sinking herself would be the point where the dredged depth of the ship channel changed from the 75' depth at the entrance nets to the 40' dredged depth maintained inside the entire area of Pearl Harbor (and no, I don't know exactly where that point was). An old fashioned "leadline" would do the trick if such depth data coukldn't be found by the Japanese in any other fashion. A sharp turn to port or starboard would place the blockship squarely ACROSS the 100yard width of the dredged ship channel with little (dredged deep water) room to spare at either end. Fore and aft anchoring would hold her in place while seacocks were opened and she settled to the bottom. Scuttling charges could certainly have been used to blow her bottoms out BUT this would NOT be desireable in terms of quickly re-opening the ship channel after Oahu fell to the Japanese.

No pilot needed, just hold to the right side of the buoyed channel until dropping the stern anchors, just before the final sharp turn to port where the bow anchors are let go.

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