Operation Mudbank

This was a programme of US naval operations against Japanese positions on the islands of Satawan and Ponape in the Caroline islands group, which were one of the Japanese bastion areas scheduled for isolation as the US forces progressed across the Pacific (29 April/1 May 1944).

Satawan is an atoll in the Mortlock islands group within the central part of the Caroline islnds group, some 180 miles (290 km) to the south-east of Truk atoll. In World War II the Japanese built a small airfield on Satawan islet.

Some versions of the 'Orange' colour-coded US inter-war contingency plan for war with Japan called for the seizure of Satawan as an intermediate base for a drive across the Pacific to relieve the Philippine islands group.

Ponape is a comparatively large island in the eastern part of the Caroline islands group. Rugged and heavily forested, it is roughly circular with a diameter of about 19 miles (30.5 km) and rises in the south central area to a maximum height of 2,566 ft (782 m). The island is surrounded by a reef and has a good anchorage.

The Japanese undertook considerable development of the island, and its inhabitants were moderately loyal to the Japanese empire, providing some hundreds of workers for other islands. By the outbreak of the Pacific War, Ponape had a seaplane base, and was protected by one coastal artillery battery and two anti-aircraft batteries. The Japanese had completed an airstrip by a time early in 1944 on an islet just to the north of the island’s capital, Colonia, on the north coast of the main island, and were working on a second airstrip.

On 12 February 1944 six Japanese flying boats staged through Ponape from the major base at Truk atoll for an attack which destroyed the US Marine Corps' main supply dumps on newly captured Roi-Namur. The Allies responded with attacks by the US 7th AAF from Tarawa between 15 and 26 February.

'Mudbank' included the shore bombardment of the Japanese military facilities on several occasions by ships including the battleships Iowa and Massachusetts, and attacks by the aircraft of the light carrier Cowpens. On 30 April a task group of nine heavy cruisers under the command of Rear Admiral Jesse B. Oldendorf undertook a gunfire bombardment of Satawan island with some 800 8-in (203-mm) and 1,200 5-in (127-mm) rounds to destroy the island’s airstrip, which was one of the primary reason why the islands of the Mudlark island group had a garrison of 753 army personnel and six medium tanks under the command of Colonel Masatake Tobita, as well as 257 naval personnel.

The bombardment of Satawan was planned and executed largely to provide the crews of the ships with a change from the constant diet of false alarms they had suffered while escorting carrier attacks. There was no return fire and the only damage seen to have been caused was the destruction of an ammunition dump and a fuel storage tank. The island was then bypassed by the Allied counter-offensive.

On 1 May Vice Admiral Willis A. Lee’s Task Group 58.7 with the battleships Iowa, New Jersey, Massachusetts, North Carolina, South Dakota and Alabama, covered by Rear Admiral Joseph J. Clark’s TG58.1 with the fleet carrier Hornet, light carriers Bataan, Belleau Wood and Cowpens, and 14 destroyers, undertook a gunfire bombardment of Ponape island, which had a Japanese garrison of about 2,000 naval personnel under the command of Captain Captain Jun Naito and 5,984 army personnel of the 3rd South Sea Detachment (later the 52nd Independent Mixed Brigade under the command of Major General Masao Watanabe.

This bombardment had been devised largely as a training exercise, for there were few worthwhile targets left on the island, and the battle line had never before operated as a unit. The island was then bypassed by the Allied counter-offensive.

These forces then headed to the east for an attack on the surviving Japanese targets in the Eniwetok and Majuro atolls of the Marshall islands group.