The battle of Manus (12-25 March 1944) saw the Americans capture the largest of the Admiralty Islands, securing their control of the massive Seeadler Harbour, which then became an important naval base for the rest of the Second World War.
The invasion of the Admiralty Islands began when American troops landed on Los Negros, the third largest of the islands, on 29 February. The island was secured by 8 March, and American attention then turned to west to the much larger Manus Island. The key part of this island was the north-eastern corner, from where the Japanese could have interfered with operations in the harbour.
Manus was to be attacked by the 2nd Brigade Combat Team, made up of the 8th Cavalry Regiment, one troop from the 7th Cavalry and various support units, for a total of 4,000 men. The attack was to be commanded by General Verne Mudge.
The invasion force arrived in Seeadler Harbour on 9 March, the day after Los Negros, the island at the eastern end of the harbour, was secured.
The first task was to capture the string of small islands that form the northern edge of Seeadler Harbour, and that could be used as artillery bases for the invasion of Manus.
The Japanese put up quite a fight on Hauwei Island, repelling a first attack on 11 March, and putting up fierce resistance to the second, successful, attack on 12-13 March.
The main target on Manus was the airfield at Lorengau, on the north-eastern coast. The airfield was located to the west of the town, near a key road junction. The coastal road (Number 3 Road) ran west from the airfield towards Lugos Mission. Number 1 Road ran west/ south-west from the airfield area into the interior of the island. Number 2 Road ran south from Lorengau town, through Old Rossun and south to new Rossun, about three miles south of Lorengau.
On 15 March US troops crossed over from Los Negros and landed at Lugos Mission, west of Lorengau. The force then split in two. The 1st Squadron, 8th Cavalry, advanced east along the coast, while the 2nd Squadron, 8th Cavalry, followed a trail south towards Number 2 Road.
The 1st Squadron ran into a strong Japanese position on the coast road. At this point the artillery on Hauwei opened fire and the Japanese were pushed back. By the end of the day the 1st Squadron was just to the west of the airfield.
The 2nd Squadron reached a position just north of the road junction by the end of 15 March. On 16 March the squadron advanced along No. 2 Road, pushing past a Japanese roadblock early in the day and reached a position south of the airfield by the end of the day.
The 1st Squadron launched an attack on the airfield on 16 March, and was close to success when a friendly fire incident forced the squadron to retreat.
On 17 March 1st Squadron, 8th Cavalry, was relieved by 1st Squadron, 7th Cavalry. The new troops launched an attack on the airfield at 10.33, but discovered that the Japanese positions had been abandoned after the preliminary bombardment. By the end of the day all three squadrons had joined, and advanced as far as the Lorengau River. On the following day the rest of the town was captured. During the final fighting in Lorengau the Americans lost seven wounded, while the Japanese suffered 87 dead.
The next American target was Rossum, south of Lorengau on Number 2 Road. This turned out to be where the Japanese had chosen to make their stand. The narrow track ran through dense jungle, making it a very strong defensive position.
On 19 March patrols from the 8th Cavalry advanced down the road and ran into heavy Japanese resistance.
On 20 March Troop F, 7th Cavalry, was rather optimistically given the task of clearing the road. They made no more progress, and suffered five dead and eleven wounded in the attempt.
21 March was spent probing the Japanese position, before on 22 March the 1st Squadron, 7th Cavalry, made a frontal assault on the Japanese positions. They advanced 500 yards at the cost of 11 dead and 29 wounded. Similar attacks on 23-24 March brought the casualty figures up to 92, and made little more progress.
The deadlock was finally broken by a large scale assault on 25 March. The 1st Squadron, 8th Cavalry, having had a few days to recover, took over. They were supported by an air attack with a mix of 500lb bombs and strafing, and a bombardment by mortars and medium tanks. The attack was also supported by armoured bulldozers that were used to fill in any Japanese bunkers. By the end of the day the Japanese positions had been overrun.
The battle for Manus had lasted for one week and had cost the US Cavalry 36 dead and 218 wounded. There were probably only around 200 Japanese troops involved in the battle, but very few of them survived.
A period of mopping up operations followed, with isolated pockets of Japanese resistance being found from time to time. The Admiralty Islands campaign was officially judged to be over on 18 May, but major operations were long over by then. The islands then became a major American based, used both to pin down the remaining Japanese at Rabaul and Kavieng, and for further advances into the Pacific.