Commodore Yosaphat "Yos" Sudarso (24 November 1925 15 January 1962) was an Indonesian naval officer killed at the Battle of Arafura Sea. At the time of his death, Yos Sudarso was deputy chief of staff of the Indonesian Navy and in charge of an action to infiltrate Dutch New Guinea. He was promoted to vice admiral (Indonesian: Laksamana Madya) posthumously.

The Battle near Vlakke Hoek (Etna Bay) of the Arafura Sea stopped an attempt by the Indonesian Navy to drop off 150 soldiers in Kaimana in Dutch New Guinea for sabotage and to incite the local population against the Dutch government. Sudarso was in charge of the operation at sea, while Colonel Murshid commanded the infiltrants. Three Jaguar-class torpedo boats left the Aru Islands in the middle of the night but were intercepted by a Dutch reconnaissance plane, as the Dutch had anticipated the action for weeks. The torpedo boats responded to the flares sent off by the plane by shooting at it. The Dutch destroyer HNLMS Evertsen then joined the scene and sunk the KRI Matjan Tutul, commanded by Sudarso. The other two ships, KRI Matjan Kumbang and KRI Harimau, fled, but one hit a reef and the other was disabled by shooting. The Evertsen was able to save most occupants of the Matjan Tutul, but at least three sailors died, among whom was Commodore Sudarso.The action itself was an abject failure and General Nasution even refused to relay the bad news to Sukarno, forcing Colonel Murshid to do this in person. However, the small battle was partially responsible for the subsequent involvement of the Soviet Union and United States in the case of Dutch New Guinea, and it is honored in Indonesia by "Sea Sacrifice Day," an annual nationwide day of remembrance. Twelve years after his death, Yos Sudarso was officially added to the register of Indonesian heroes of the Revolution. Indonesia issued a special postage stamp to commemorate his service to his country, while the KRI Harimau was made into a monument at Purna Bhakti Pertiwi Museum in Taman Mini Indonesia Indah.

Indonesia's Yos Sudarso Island and Yos Sudarso Bay are named in his honor. There are two Indonesian Navy ships named after him. The first ship was KRI Jos Sudarso (351), a Riga-class frigate commissioned in 1963 and retired in 1986. The second ship is an ex-Dutch Van Speijk-class frigate named KRI Yos Sudarso (353) which is still active in the fleet today.

Netherlands New Guinea (Dutch: Nederlands-Nieuw-Guinea, Indonesian: Nugini Belanda) was the western half of the island of New Guinea while it was a part of the Dutch East Indies until 1949, later an overseas territory of the Kingdom of the Netherlands from 1949 to 1962. It was commonly known as Dutch New Guinea. It contained what are now Indonesia's two easternmost provinces, Papua and West Papua, which were administered as a single province prior to 2003 under the name Irian Jaya, and now comprise the Papua region of the country.

During the Indonesian Revolution, the Dutch launched a police action ("Operation Product") to capture territory from the Indonesian Republic. However, the harsh methods of the Dutch had drawn international disapproval. With international opinion shifting towards support of the Indonesian Republic, the Dutch managed in 1949 to negotiate for the separation of Netherlands New Guinea from the broader Indonesian settlement, with the fate of the disputed territory to be decided by the close of 1950. However, the Dutch in coming years were able to argue successfully at the UN that the indigenous population of Netherlands New Guinea represented a separate ethnic group from the people of Indonesia and thus should not be absorbed into the Indonesian state.

In contrast, the Indonesian Republic, as successor state to the Netherlands East Indies, claimed Netherlands New Guinea as part of its natural territorial bounds. The dispute over New Guinea was an important factor in the quick decline in bilateral relations between the Netherlands and Indonesia after Indonesian independence. The dispute escalated into low-level conflict in 1962 following Dutch moves in 1961 to establish a New Guinea Council.

Following the Vlakke Hoek incident, Indonesia launched a campaign of infiltrations designed to place pressure on the Dutch. Facing diplomatic pressure from the United States, fading domestic support and continual Indonesian threats to invade the territory, the Netherlands decided to relinquish control of the disputed territory in August 1962, agreeing to the Bunker Proposal on condition that a referendum to determine the final fate of the territory be conducted at a later date. The territory was administered by the UN temporarily before being transferred to Indonesia on 1 May 1963. A plebiscite, the Act of Free Choice, was eventually held in 1969, but the fairness of the election is disputed.