The landings at Sansapor (30-31 July 1944) were the last major American offensive of the long New Guinea campaign, and saw them capture a foothold on the Vogelkop Peninsula, at the western end of New Guinea, where they were able to build a medium bomber base to support operations further west.
Sansapor was only the last in a series of areas considered for the Allied landings on the Vogelkop. The key factor was the availability of suitable land for airfields, and this caused the abandonment of earlier plans. Sansapor became of interest in mid-June, especially after the most recent potential target, at Waigeo, was dismissed on 21 June.
Sansapor is located on the north-west coast of the Vogelkop Peninsula, seventy miles north-east of Sorong, the original American target and 60 miles east of Waigeo. The aim was to build airfields in the area around the neighbouring villages of Sansapor and Mar.
Early aerial photography suggested that Sansapor was no better than the earlier targets, but on 23 June a submarine landed a scouting part near Mar, and they found a couple of possible locations for airfields. Their report was delivered on 30 June. On the same day MacArthur issued orders for an attack on Sansapor, to be carried out one month later, on 30 July. Fortunately the invasion force, Alamo Force, already existed, having been created for the Sarong and Waigeo plans.
The attack was to be carried out by most of the 6th Infantry Division, supported by anti-aircraft units. The Japanese weren’t present in large numbers, but they did have a barge staging post at Sansapor, and were reported to be based at a nearby plantation. The plan was to land at Mar, twelve miles east of Sansapor, and hopefully catch the Japanese by surprise.
Two separate landings were conducted on 30 July. A small party landed on Middelburg Island, just off the coast to the north-east of Mar. Later in the same day the same force moved north to occupy Amsterdam Island. Neither of these landings was opposed.
The main landings took place at Red Beach, about a mile and a half to the east of Mar. Three battalions were involved. The 1st and 2nd Battalions landed first, starting at 7.01am and created a beachhead. The 3rd Battalion landed at 7.40am, and advanced west, reaching Mar without running into any resistance.
On 31 July the 3rd Battalion was shipped west along the coast to Green Beach, just short of Sansapor. They then advanced south and occupied the village. The small Japanese garrison had fled, and once again the attack was unopposed.
During August the Americans conducted patrols that reached ever further from the beachhead. On 3 August they captured 92 sick or wounded Japanese troops in a hospital, and in some minor fighting captured 23 and killed 4. In mid-August a sizable Japanese force was discovered heading west towards Kor. This wasn't a response to the landings, but was instead a regular movement along the coast. The Japanese troops were the headquarters personnel of the 35th Division, taking part in an evacuation of the former Japanese base at Manokwari.
The Japanese had no intention of attacking the American position at Sansapor and instead attempted to bypass them. This effort failed, and by the end of August the Americans had killed 155 Japanese and captured 42 on their eastern flank, and killed 197 and captured 154 to the west. By 31 August the Americans had only lost 14 dead and 35 wounded.
Work on the airfields was soon underway. The airfield on Middleburg Island was completed by 17 August, and a second strip parallel to the coast east of Mar was ready by 3 September.
The Japanese did make some attempts to attack the new airfields from the air. The first sizable attack came on 25 August and saw one US fighter destroyed on the ground. A larger raid on the night of 27-28 August destroyed four P-38s. but a third raid on 31 August was less effective.
After August there were very few clashes with Japanese troops. Most of the Japanese remaining on the Vokelkop had withdrawn to the south-eastern corner, where more food was available, while the few remaining in the north didn’t stray far from their bases.