Operation Cherry Blossom: The Invasion of Bougainville

The overarching Allied operation in the Solomon’s Campaign was Operation Cartwheel, the isolation and eventual capture of Rabaul on the island of New Britain, Imperial Japan’s main base in the South Pacific. The previous capture of New Georgia and other northern Solomon Islands placed Rabaul within heavy and medium bomber range, but shorter ranged fighters and naval bombers needed airfields closer. The island of Buka, just north of Bougainville was the obvious choice, but Adm Halsey decided that the flat areas of the much larger Bougainville were enough to provide the airfields necessary for the eventual isolation of the islands, while doing the same to Rabaul.

On 1 November 1943, Halsey launched Operation Cherry Blossom, the invasion of Bougainville. The initial landings at Torokina on the west coast of the island were virtually unopposed: only a single Japanese platoon was in the area. Gen Hyukutake of the Japanese 17th Army gambled that Halsey would invade Buka off the northern tip of Bougainville and bypass Bougainville entirely. He chose wrong. Nonetheless, he and the naval commander at Rabaul, Adm Kusaka, rushed men and ships to the area to seal the beachhead and eventually reduce it with naval gunfire and ground attack. They knew from their experience at Guadalcanal that if the Allies got a secure beachhead with a functioning airfield, the Americans were almost impossible to dislodge, especially as American naval surface warfare proficiency had come leaps and bounds since the precious year. The Americans knew it also.

In the shadow of Mt Baranga, an active and smoking volcano, Allied transports rushed to unload. 30% of the initial 3rd Marine Division landing force, including three SeaBee battalions, assisted with unloading the transports in order to get them safely away before the inevitable Japanese naval sortie arrived. The Japanese attempted to imitate their success at Savo Island the year before, but Adm Aaron Merrill’s Task Force 39 was waiting for them and savaged the Japanese at the entrance to Empress Augusta Bay off the west coast of Bougainville. Nevertheless, Halsey was concerned.

Though a brilliant operational commander and leader of men, he still thought in year old archaic terms for naval superiority, i.e. CV>BB>CA>CL>DD. He, and to be fair the rest of the US Navy, still hadn’t grasped that the Japanese’ most damaging weapon was the Long Lance torpedo on their small destroyers, and that the quick firing radar controlled 6” guns on the American light cruisers were far superior to the big manual 8” heavy cruiser guns. He saw the reports that the Japanese had heavy cruisers and that he didn’t so he ordered Task Force 38, his only carriers, to strike Rabaul and sink any shipping that could interfere with the invasion of Bougainville. He specifically tasked them to drive away the heavy cruisers to protect his transports and their escorts and to prevent another “Hell Night” as had happened on Guadalcanal. He was successful in his gamble, but only because he was ignorant of the Japanese lack of carrier-borne pilots. Halsey thought he might be sailing into a “reverse Midway”, but Kusaka had no way to strike Halsey’s carriers and the land based planes were committed over Bougainville. Kusaka withdrew his ships back to Truk, the main Japanese anchorage in the South Central Pacific and out of the fight. No further Japanese attempts to interfere with any Solomon Island were to occur for the rest of the war. The Naval Battles of the Solomon Island, which began so ignobly off Savo Island 17 months before, ended in a decisive American victory.

After the failed Japanese attempts to destroy the beachhead by sea, the US 3rd Marine and US Army 37th Infantry Division expanded the beachhead over the next few weeks. Navy SeaBees started construction of an airfield literally just off the beach, and quickly began building roads inland. They built them so fast that Marines told them to slow down as their roads were pushing farther forward than the Marine pickets. By the end of November 1943, the Japanese increased their counterattacks, and had occupied the hills around the beachhead with artillery, despite several serious losses against counter-counter attacking Marines in the perimeter. First, the entire initial naval landing force sent by Kusaka at the onset of the invasion was wiped out at Koromokina Lagoon on 7-8 November, and an entire Japanese regiment was destroyed at Piva Forks later in the month.

In December 1943, the 3rd Marine Division was replaced by the veteran US Army Americal Division, and they and the 37th expanded the perimeter to prevent artillery fire from molesting Empress Augusta Bay and the three airfields under construction. The first aircraft to land of the newly operational beach airfield was a corsair from the famed VMF 214, the “Black Sheep” squadron, on 11 December. Within hours, Maj. “Pappy” Boyington and his fighters did a sweep over Rabaul, just because they could, and taunted the surprised Japanese to come up after them. The Japanese knew the Allies were building airfields on Bougainville but completely misjudged the speed at which the SeaBees could construct one under fire. Though until all three airfields were completed, the fighters more often than not flew ground attack missions in support of marines and soldiers fighting a few hundred yards from the flight line. The operational airfields finally convinced Gen Imamura at Rabaul, Hyukutake’s boss, that Halsey’s main effort wasn’t coming at Buka.

Imamura was convinced all throughout November and December that Halsey would attempt to seize Buka, and he wasn’t wrong, he just had the timing incorrect. (Buka was Halsey’s next target after the airfields on Bougainville were completed.) Imamura assumed Halsey knew about the severe Japanese shortage of carrier qualified pilots, and would use his own carriers to support a bold landing on Buka, bypassing and isolating Bougainville and getting that much closer to Rabaul if successful. However, Halsey was unaware of the pilot shortage and assumed the carriers were still out there lurking, waiting to pounce. To Halsey, Buka was too exposed and not worth the risk; a risk which Imamura assumed the legendarily aggressive Halsey would take. Once the Black Sheep and other fighter squadrons did their sweeps over Rabaul, Imamura could no longer ignore the danger the airfields posed. He released troops from Buka and northern Bougainville to reduce the growing Allied perimeter at Torokina. But Imamura’s assault was now substantially more difficult, Halsey’s two US Army divisions had time dig in and stockpile necessary supplies.

Nevertheless, the Japanese troops encountered so far in the battle were relatively few compared to what Imamura had on hand. It took Hyukutake nearly two months to stage Imamura’s reinforcements in their assault positions around Torokina. In March, Halsey’s perimeter on Bougainville would feel the entire weight of Hyukutake’s 17th Army.

To be continued…

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