This thread deals with the question:
Could the Japanese have taken Oahu? I think the answer is that they could have, though the enterprise by no means was a 'sure thing'. I will attempt to detail what a successful invasion of Oahu might have looked like, culminating in a draft operational order for an AH all-out IJN attack on Oahu for 7-9 December 1941.
Operational objectives of a landing.
The purpose in landing on Oahu would be to exacerbate the effects of a blockade conducted mainly by airpower from the other islands. Airpower on its own could not prevent the flow of material from the continent to the embattled island, and it is probable that the combination of existing stores on Oahu and those that could be delivered (albeit, at heavy loss in Allied transports) would suffice to prevent a surrender. The most effective means by which this final lifeline could be cut would be to land troops on Oahu and physically occupy positions which would prevent the resupply of the garrison and the civilians on the island.
The deep water ports by which Oahu could be supplied would be Pearl Harbor, Honolulu, and Kaneohe Bay. Should these windpipes be captured or cut, then the the only recourse remaining to the defenders would be to attempt a resupply effort under hostile skies for an army corps and 300,000 people over whatever beaches remained -an impossible task once the existing stockpiles were depleted.
The purpose of a landing would be to achieve the physical occupation or interdiction of, Kaneohe Bay, Honolulu and Pearl Harbor.
Selection of the initial landing site.
Oahu's four shores were not created equal in their usefulness towards facilitating the capture or interdiction of the three Oahu ports. The north shore is the most easily dismissed as a potential landing site. Weather conditions are unrealizable at best and suicidal at worst. The north shore is not anywhere near Kaneohe, Pearl or Honolulu and the route of march via Schofield is easily blocked. It also has a dedicated divisional defense backed by plenty of artillery.
The south shore is also out for the initial landing. While moving in here gains direct access to the entrance to Pearl Harbor and Honolulu, and the weather conditions tend towards superlative, the defenses deployed to contest a landing here were so fearsome that even a division-level assault would probably fail. Furthermore, the available anchorages on the south shore were not such that transports could disembark outside the range of coastal artillery.
The west coast was attractive for a landing on a number of levels. The weather here was the best available, on average (south excepted). The defenses along the west shore weren't of a sufficient strength to prevent a landing. But while the Japanese could undoubtedly get ashore, it is questionable whether they could break out of the difficult mountains that isolate it from the central plain. Without a breakout onto the central plain, the tactical objectives necessary to fulfill the operational conditions of a surrender could not be met - all three harbors on Oahu would still be in American hands and available to unload supplies.
By process of elimination, the invasion occurs on the east coast. The weather, while not as good as along the south, is acceptable. The defenses on the east coast were insufficient to prevent a division-scale landing. An important operational objective could be captured immediately at Kaneohe Bay (with Bellows Field thrown in as an additional bonus). Finally, a second operational objective (Honolulu) was close at hand to the east shore.
Tactics.
Honolulu is the key to the island because from Honolulu communications to and from Pearl Harbor can be interdicted. Because of a quirk of geography, Oahu's premier city and important source of supplies is positioned on the peninsula on the southeast corner of the island. This peninsula in turn is dominated by the Koolau range mountains, which in turn are accessible from sparsely defended Kaneohe Bay. If the Japanese could occupy Honolulu via Kaneohe, then the civilians and garrison of Oahu would be thrown back onto the central plain, largely cut off from the sea with the loss of much of the supplies housed in the city. From Honolulu entry of supply ships into Pearl Harbor could then be prevented, meaning that the conditions necessary for a surrender - the dislocation of the defenders from their base of supply and access to overseas resupply - would have been achieved.
The enclave at Kaneohe, however, is on the wrong side of the Koolau Range, meaning that the attackers would have to traverse very difficult terrain in order to make an approach on Honolulu. In contrast, the defenders could access positions to block this movement more easily, via the landlink that connects Honolulu to Pearl Harbor. It is more likely than not that a fighting front would stabilize short of Honolulu. As predicted by the American army before the war, it is probable that the mountain barrier, so useful to the Japanese in their initial landing, would prevent the capture of Honolulu.
The proposed tactical solution to the problem of the mountain barrier blocking access to Honolulu, Pearl Harbor, and the other bases is to land the IJA 1st Artillery Regiment at Kaneohe with about 105 long range guns and plenty of ammunition, such that all positions on Oahu (except Ewa) could be pounded via saturation artillery barrages from the east side of the island using spotters situated in the mountains and aided by aerial reconnaissance operating from the other islands.
Noteworthy IJA artillery types for the OOB of the 1st Regiment:
www3.plala.or.jp/takihome/artillery.htm
Type.......................Calibre.....Range.....Qty.....Weight......Tar
Model 95(1935)........75mm.....11,700.....261......2,450..........1
Model 90(1930)........75mm.....15,310.....786......3,100..........1
Model 91(1931).......105mm....11,810....1100.....3,300..........1
Model 92(1932).......105mm....19,910.....180......8,220..........2
Model 96(1936).......150mm....12,910.....440......9,130..........1
Model 89(1929).......150mm....21,000.....150......23,000........2
24cm......................240mm...15,310......80.......83,900........1
(Tar - targets are all bases can be reached by this weapon.)
1 = Koko Head to Honolulu plus Aliamanu Crater
2 = All targets in no. 1 plus Wheeler, Schofield, Naval Base, Hickam, Ford
The initial allocation of ammunition for 1st Artillery Regiment's artillery offensive in Tinkerbell is in the order of 185,000 75mm-240mm shells. In comparison to other Japanese island campaigns, this was a heavy commitment (3 times that of the Philippines and 53 times greater than the trickle that reached Guadalcanal),
http://www3.plala.or.jp/takihome/artillery_history.html
Japanese shell usage vs. allocation for Tinkerbell (Phase I).
Type...............Philippines.........Guadalcanal....Oahu (Phase I)
75mm..............24,996......................1,520.............80,000
100/105mm......14,749.......................742...............48,000
155mm............19,736......................1,129.............48,000
240mm.............4,042..........................0.................6,000
Sequence.
The initial landings by the 16th and 48th I.D. secure beach heads on the east coast of the island, capture the deepwater port at Kaneohe, and attempt to cross the mountains to attack Honolulu. The heavy guns of the 1st Artillery Regiment would then be landed at points along the east shore to conduct an artillery offensive aimed at destroying the bases in the interior. The coastal defenses protecting Honolulu would be destroyed by a protracted air and artillery barrage over the course of weeks. With these defenses removed, 2nd I.D. then makes a direct assault on Honolulu with 16th and 48th in support. If successful, then 1st Artillery can re-deploy elements to Honolulu and bombard Pearl Harbor. Four divisions (16th, 48th, 2nd, 7th) are available to continue the offensive onto Hickam and into the naval base.
Landing at Kaneohe
The landing force attacking Kaneohe consists of 29,500 men, 86 artillery pieces, 54 mortars and 300 vehicles, plus some rough-terrain pack mules and supplies. A total of 3,233 Diahatsu equivalents is required to land everything. This force is transported from Japan to the Marshall on 34 transports with an inherent unloading capability of 245 Diahatsu equivalents per run (34*5 = 170 Diahatsu equivalents).
In addition, the 1st Artillery Regiment of 1,256 Diahatsu loads aboard 14 transports (70 Diahatsu equivalents) awaits landing as reinforcements.
Tinkerbell increases the 'punch' of the landing forces by means of attaching the now empty first-wave transports to the invasion forces while all are laying over in the Marshall Islands awaiting the replenishment of the carriers after December 22nd, and also by way of a specialized Diahatsu carrier force. The Hawaii transports (29 ships) add another 145 Diahatsu equivalents (max) to the landing force, plus another 52 in the Diahatsu carrier force - for a grand total of 437 Diahatsu equivalents aboard 80 transport ships. In addition, 7th Infantry will have assembled more transportation assets commandeered from the local economy. The transport force requires 10.27 loads per Daihatsu equivalent to completely disembark the two divisions and the artillery regiment.
From the weather landing tables (see
unloading), the average east coast conditions are:
Infantry: 75% efficiency
Light artillery: 39% efficiency
Heavy equipment: 25% efficiency
Load/unload times are budgeted at 30/30 minutes under normal conditions. This is higher than the USMC doctrine,
Time to Load.--The loading times in the tables are based upon debarking under average conditions, using cargo nets over the side of the transports in place of ladders and gangways. An allowance of about 50 percent has been made for delays which are expected under war conditions. the time given includes delays incident to placing the boat alongside transports. The time of loading a boat will carry according to the relative amount of personnel and materiel comprising the load, the facilities of the transport for discharging, the training of the personnel, and the condition of the sea...
http://www.ibiblio.org/hyperwar/USA/ref ... 31-5-1.htm
Landing Plan.
Prepatory aerial bombardments commence several weeks prior to invasion (22nd, 23rd, 24th Air Flotillas). Attacks will be dispersed across entire island. Pre-landing bombardments commence 48 hrs prior to landing.
Invasion fleet will demonstrate to the south of Oahu, then pass close to Molokai and travel northwest into designated anchorages off east coast. 16th and 48th Division will land in the Kaneohe Bay region at about 0100 with an initial landing force of around 9 battalions (over 10,000 men). 2/3rds of the force will land south of Kaneohe NAS, 1/3rd north of it. Battalion landing zones are 2,500 yards wide, to disperse defending artillery.
Advanced infantry elements will rapidly penetrate inland, seeking the mountain passes to the southwest, with the ultimate objective of Honolulu. Unit organization at this point would be problematical above the company level, improving as time went on. Despite the seizure navigational reference points, it is expected that attack units will make errors and intermingle. When such navigational problems occur, units will adapt the mission appropriate to their landing location, not their original orders.
Transports will remain outside the 600 foot depth curve until waters closer to shore have been swept of mines.
Transports in south will maintain 40,000+ yard separation from batteries Williston and Hatch from daylight (if these are operational), such that they can rapidly draw out of range if they come under fire. Anticipated range to coastal batteries are:
Williston/Hatch (16") - 35,000 - 39,000 yards.
Closson (12") - 25,000
Randolph, Granger (14"/8" ) - 21,000 / 22,000 yards.
Transport anchorage will be screened at night by smoke.
If the long range guns are already destroyed, then this restriction does not apply, and transports can approach to the 600 foot curve.
Navy SNLF patrol boats will make diversionary landings:
2 (450 men) on Oahu, west coast.
1 (225 men) on Oahu, south coast
1 (225 men) on Oahu, north coast
Remaining Navy SNLF patrol boats will attack in southern sector of east coast near Koko Head.
Battalions in first wave: 9, plus 2,250 SNLF troops = 13,050.
IJA battalion composition: 1,200 men, 70MG, 2 tanks, 18 artillery pieces/mortars, 4 AT guns, 35 x 50mm knee mortars, 5 flamethrowers, 6 vehicles, ammunition, food.
Prepatory Missions.
Unit: Kido Butai.
Date: Commencing X-2.
Mission: Bombardment.
Primary targets: Land based air power. Naval power.
Secondary targets: Coastal defenses. Communications.
Landing day assignment: Counterbattery. Fire support. Deep interdiction.
Unit: Surface naval forces.
Period: Commencing X-2.
Mission: Bombardment
Primary targets: Coastal defenses, Communications choke points and infrastructure. Enemy reserve positions.
Secondary targets: Land based air power. Naval power.
Landing day assignment: Counterybattery. Fire support. Deep interdiction. Force protection.
Interdiction mission is to prevent main defending forces from interfering with the attack on Honolulu. See bombardment zones depicted on map.
Unit: 7th Infantry Division.
Period: X Day or X-1.
Mission: Capture several small islands off east coast of Oahu. Prepare these to function as navigational reference points for subsequent invasion waves.
Unit: 24th, 22nd, 23rd Air Flotillas.
Period: Commencing X-21
Mission:
Reconnaissance: Provide targeting information on Oahu's coastal defenses, defensive positions, aerial forces, supply bases, communications, power generation.
Bombardment: Coastal defenses, air bases, naval base, defensive positions, supply bases, communications, power generation.
Blockade: Maintain surveillance towards United States west coast. Identify and attack reinforcements attempting to contest blockade.
Unit: 6th Fleet (submarines).
Mission: Blockade, surveillance.
Period: Commencing mid December.
Using forward base of operation established at Maui, commence deep patrols off US West Coast (primary target: aircraft carriers). Maintain blockade (local patrols).
Duration.
Preliminary bombardment: 2 days.
Landing: 3 days.
Contingency: If weather conditions prevent the total debarkation of invasion force at Oahu, then residual elements will unload at Maui, and then these elements will stage to Oahu via Molokai. Prior to departure, transport force will provide any addition resources necessary to lift from Molokai to Oahu.
Landing details.
http://www.soest.hawaii.edu/coasts/data ... photo.html
Beach 1
Kailua Beach, Bellows Beach, Waimanalo Beach (a stretch of about 8 miles)
http://www.soest.hawaii.edu/coasts/data ... es/112_wai
manalo_beach.jpg
http://www.soest.hawaii.edu/coasts/data ... es/113_wai
manalo_beach.jpg
Landing force:
4 battalions (4,800 men), plus supporting equipment.
160 Diahatsu equivalents.
Approach to beach: 8,600 yards.
Time to/from beach: .9 hr
2nd Wave arrival time:
Infantry: 3.8 hours
Light artillery: 7.5 hours
Heavy artillery: 11.8 hours
Navigational markers occupied to assist wave navigation.
Small islands Kaohikaipu and Manana
http://www.soest.hawaii.edu/coasts/data ... ana_is.jpg
Objectives:
1) Capture Bellows Field
2) Advance on Koko Point to make contact with SNLF forces landed there.
3) Advance inland towards Honolulu.
Beach 2:
http://www.soest.hawaii.edu/coasts/data ... kailua.jpg
Landing force:
2 battalions (2,400 men), plus supporting equipment.
80 Diahatsu equivalents.
Approach to beach: 7,600 yards.
Time to/from beach: .75 hr
Objectives:
1) Capture Kaneohe Bay Naval Air Station
2) Advance inland and capture high passes.
2nd Wave arrival time:
Infantry: 3.3 hours
Light artillery: 6.4 hours
Heavy artillery: 10 hours
Navigational markers occupied to assist main waves:
Small island: Mokulua, Mokomanu
http://www.soest.hawaii.edu/coasts/data ... slands.jpg
http://www.soest.hawaii.edu/coasts/data ... anu_is.jpg
Beach 3, 4, 5
Beach 3:
http://www.soest.hawaii.edu/coasts/data ... io_pts.jpg
Beach 4:
http://www.soest.hawaii.edu/coasts/data ... na_bay.jpg
Beach 5:
http://www.soest.hawaii.edu/coasts/data ... aluula.jpg
Landing force:
3 battalions (360 men), plus supporting equipment.
120 Diahatsu equivalents.
Approach to beach: about 5,500 yards.
Time to/from beach: about .55hr
Objectives:
1) Advance south of Kaneohe Bay and capture high passes inland.
2) Assist in capture of Kaneohe Bay NAS.
3) Advance north, west along coast as far as possible.
Beach 6
Landing force: 4 SNLF patrol boats (900 men)
Objectives: Capture Koko Head. Advance towards Honolulu.
2nd Wave arrival time: None.
Beach 7
Landing force: 2 SNLF patrol boats (450 men)
Objective: Advance towards Diamond Head.
2nd Wave arrival time: None.