Treasury Island Landings
If the initial plans for the direct assault on the Buin area or the Shortlands had been carried out, the two small islands of the Treasury Group would have been bypassed and left in the backwash of the campaign. Instead, with the change in plans to strike directly at Empress Augusta Bay, the islands of Mono and Stirling became important as long-range radar sites and torpedo boat anchorages. Moreover, in an attempt to deceive the enemy as to the direction of the attack on Bougainville and convince him that the ultimate Allied aim might be the Buin area or the Shortlands, the seizure of the Treasurys was given added emphasis by being set as a preliminary to the Torokina landings. To help this deception succeed, reconnaissance patrols to the Shortlands and diversionary operations on the island of Choiseul–plus low-flying photo missions over the Shortlands–were scheduled by IMAC to increase the enemy’s conviction that the follow-up objective was the Shortlands.
This could have been a natural assumption by the enemy. The Treasurys are about 60 miles northwest of Vella Lavella and only 18 miles south of the Shortlands. While the size of the Treasurys limited consideration as a major target, Mono and Stirling were close enough to Shortland Island to cause the Japanese some concern that they might be used as handy stepping stones by SoPac forces. But then again, the Treasurys are only 75 miles from Cape Torokina–a fact which the Allies hoped might be lost on Bougainville’s defenders.
The Treasury Islands are typical of other small islands jutting out of the sea in the Solomons chain. Mono is a thickly forested prominence of volcanic origin, with abrupt peaks and hill masses more than 1,000 feet high in the southern part. These heights slope gradually in an everwidening fan to the west, north, and east coasts. The shores are firm, with few swamps, and rain waters drain rapidly through deep gorges. The island is small, about four miles north to south and less than seven miles lengthwise.
Stirling Island to the south is smaller, more misshapen. Fairly level, this island is about four miles long and varies from 300 yards to nearly a mile in width. There are several small, brackish lakes inland, but the island is easily traversed and, once cleared of its covering forest, would be an excellent site for an airfield. Between these two islands is a mile or more of deep, sheltered water–one of the many anchorages in the Solomon Islands to bear the name Blanche Harbor. The combination of these features–airfield site, radar points, good anchorage–was the factor which resulted in the seizure of the Treasurys as part of the Bougainville operation.
Opening excerpt and map from “Isolation of Rabaul”, History of U.S. Marine Corps Operations in World War II, Historical Branch – U.S. Marine Corps – Chapter 2
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