Savo Island

[Carl Schwamberger]

I would assume the Marines were accompanied by a CB detachment that did the same sort of surveying on the island itself.

Probably, tho map making was under the G2 or intel section of the USN & Marines. The existent maps found from Commonwealth sources were somewhat up dated from the photo recon mission run a few weeks before the landing. Those confirmed a lot of details for the construction of the airfield, but gave up little or nothing on what was under the canopy of dense brush and forrest. Ashore the artillery had a robust survey capability, but it was narrowly trained & a full blown 5th order survey would have been problematic. Up dates were ongoing, mostly from further air photography and reports from ground reconnaissance. Edsons Long Patrol with the Raider Battalion clarified what lay beyond the perimeter south of the airfield. When the HQ 14th Corps was established it brought a more robust map making capability.

After a few months working with the US forces and becoming familiar with the language of the US maps the native scouts employed by the Marine were able to provide valuable information about the ground the Japanese occupied to the West.

[T. A. Gardner]

The US naval base over on Tulagi Island, et al., was no small operation. By the end of 1942 into early 1943 it included a PT boat base with a small tank farm for fuel housing 4 PT squadrons and 24 boats, 3 subchaser squadrons with 12 boats, a seaplane base for PBY's, a landing craft base, and the naval base itself.
Included in the usual smaller ships and craft present included:

24 PT boats
12 SC (subchasers)
3 YP (large tuna trawlers that were prized as cargo carriers having a large refrigerated capacity)
1 YN (net layer)
1 YT (small tug)
6 APD (these were regular visitors as they were able to evade the IJN most of the time)
1 AN
8 AM (auxiliary minelayers)
1 ASR (small repair ship)
1 AGP (a patrol yacht)
4 AT (ocean going tugs)
1 AO (a small oiler)
1 AGS (survey ship)
2 small floating drydocks

This base came under very sporadic air attack during the campaign and the Japanese never made any real attempt to eradicate it. It became a refuge for badly damaged warships where they could fix the worst of their damage and then sail to Espirto Santo for further repair or back to Pearl Harbor. More than one US warship was salvaged and saved by this base's presence.
It also gave a location for transports to unload in relative safety with their cargos then transferred to Guadalcanal by YP or landing craft.

[jbroshot]

Probably, tho map making was under the G2 or intel section of the USN & Marines.

There was a mapping and reproduction section in the Headquarters and Service Company of the Marine engineer battalion. At least that's where it was in 1944.

[Carl Schwamberger]

The did the printing and part of the other grunt work. The decisions on what to map out ect.. came out of joint requirements made by the G2 & 3 with the G2 having direct responsibility for the overall map provision. Wherever the mapping section physically was on the naval base or Marine positions on the ground the chief of the mapping section was ultimately accountable to the G2. Support functions are frequently like that. ie: in the artillery battalion the Survey Section is part of the HQ company & the company commander is responsible for ensuring the have rations, fuel in their vehicles, and ammo in their weapons, but for mission tasks the S-3 is running them.

[Carl Schwamberger]

... Yes, the Ichiki detachment was about the only immediately available force, but the IJA didn't order Ichiki to wait until he was reinforced before engaging the US in combat. They let him land and launch a hasty assault on the US positions getting his forces wiped out. It was really just arrogance and over confidence on the IJA's part.

I may be over thinking this, but there may have been something more nuanced in the LtCols thinking.

Franks in his analysis if the Guandalcnal campaign commended Vandigrift for not following current US doctrine and the original plan for the defense of the airfield. He directed a much more compact and linear defense, eschewing a broader defense area, and strong points spread out more. Instead he ordered the denser defense positions closer into the airfield. It could be Ichikis reconnaissance found Marines on the east side of the airfield where they would logically be were the landing force only 5000 men. Following standard tactics of the era a 10,000+ man landing force would have placed their defense further out & further to the east. Ichikki looked at the information at hand, the actual position of the Marines defense & saw it confirming the assumption of a small enemy force.

[Takao]

Certainly a possibility

[T. A. Gardner]

... Yes, the Ichiki detachment was about the only immediately available force, but the IJA didn't order Ichiki to wait until he was reinforced before engaging the US in combat. They let him land and launch a hasty assault on the US positions getting his forces wiped out. It was really just arrogance and over confidence on the IJA's part.

I may be over thinking this, but there may have been something more nuanced in the LtCols thinking.

Franks in his analysis if the Guandalcnal campaign commended Vandigrift for not following current US doctrine and the original plan for the defense of the airfield. He directed a much more compact and linear defense, eschewing a broader defense area, and strong points spread out more. Instead he ordered the denser defense positions closer into the airfield. It could be Ichikis reconnaissance found Marines on the east side of the airfield where they would logically be were the landing force only 5000 men. Following standard tactics of the era a 10,000+ man landing force would have placed their defense further out & further to the east. Ichikki looked at the information at hand, the actual position of the Marines defense & saw it confirming the assumption of a small enemy force.

I don't think so. I think Ichiki was basing his decisions on his combat experience in China. That is, he expected the Marine defenders to be armed primarily, or entirely, with rifles. Support weapons would be few in number and poorly utilized. His expectation was once his men closed with the enemy they would flee. That was what he was used to from China, and he had no understanding of how US Marines would vary from that scenario.
If you look at his combat command experience, he was extremely aggressive while being dismissive of his enemy.
What he ran into was a buzzsaw of interlocked machinegun fire, canister from 37mm guns, then artillery fire and tanks. It was completely different from what he would have expected.

Ichiki knew that there were between 2 and 10,000 US troops on Guadalcanal, that's what his higher command told him. So, he knew he was facing a superior force in numbers. Yet, he still chose to lead a frontal attack on the Marine defense perimeter the first chance he got. Interestingly, Ichiki had sent his communications officer forward with a 38 man scouting party that ran into a Marine scouting party (about 60 men) who pretty much wiped the Japanese out, five men escaping to report the loss to Ichiki. His officers thought he should delay his attack and wait for reinforcement only to be dismissed and the plan carried forward.

[Takao]

To add this part of an old WW2F post of mine...


Now comes the fly in the ointment...
A large Marine patrol comes across Ichiki's commo outfit laying phone wire, and attacked, killing most of them. Amongst the captured items were several detailed maps showing the Marine defenses & Ichiki's plan of attack the weak defenses of the Tenaru/Ilu River. When the patrol returned with their finds, Vandegrift immediately strengthened those particular defenses.

Thus, when Ichiki hit the area, it was not a weak spot, but a strong point.

[T. A. Gardner]

To add this part of an old WW2F post of mine...


Now comes the fly in the ointment...
A large Marine patrol comes across Ichiki's commo outfit laying phone wire, and attacked, killing most of them. Amongst the captured items were several detailed maps showing the Marine defenses & Ichiki's plan of attack the weak defenses of the Tenaru/Ilu River. When the patrol returned with their finds, Vandegrift immediately strengthened those particular defenses.

Thus, when Ichiki hit the area, it was not a weak spot, but a strong point.

Even if that hadn't happened, the Marines would have reinforced with more infantry and tanks and they had artillery support. Ichiki and his detachment would still be annihilated.

[Carl Schwamberger]

Tho in that case the Japanese infantry companies probably would have made it across the river & beyond before being halted. The character of the battle would have been less a full blown massacre of a frontal attack. In this case the Marines would have been first reinforcing a defense under a ongoing attack, then using their remaining reserve to execute a counter attack. US doctrine of the time was to seek and attack the enemy flank. So, as with OTL the tanks and a body of infantry would have been aimed at the Japanese left or inland flank. In the end the battle would have resembled the September fight on Edsons Ridge.