Uthman was appointed governor of
Bahrayn (eastern Arabia) and
Oman (southeastern Arabia) by Umar in 636, following the dismissal of
al-Ala al-Hadhrami. The province of the
Yamama (central Arabia) was administratively attached to Bahrayn at the time. Uthman was permitted by Umar to nominate his brother al-Hakam as his replacement in Ta'if. Uthman dispatched naval expeditions against the ports and positions of the
Sasanian Empire and further east to the borders of India. The first Arab naval raids against the ports of the Indian subcontinent were carried out on the orders of Uthman. According to the history of
al-Baladhuri, the raids targeted
Thane (near modern Mumbai),
Debal and
Bharuch. The assault on Thane, the first Arab raid in India, was commanded by Uthman's brother al-Hakam and was a success, the Arabs returning to Oman without incurring any fatalities. The following raid on Debal was commanded by another brother, al-Mughira. Al-Hakam led the raid on Bharuch. The raids were launched in according to al-Baladhuri. The modern historian
Nabi Bakhsh Khan Baloch suspects that if the raids against the Indian coast were actually undertaken, they likely occurred in late 636. The naval operations were launched without Umar's sanction and he disapproved of them upon learning of the operations, citing his fear for the safety of Arab troops at sea. The contemporary Armenian historian
Sebeos confirms these Arab raids against the Sasanian littoral. According to Baloch, the reasons for Uthman's initiative are not identified by the medieval sources and were possibly zeal-driven adventures for the cause of
jihad (holy struggle). In 637 Uthman was recalled from Bahrayn by Umar and reappointed to Ta'if, likely as a consequence of his unilateral launch of naval raids against India. He was restored to Bahrayn in 638 in the aftermath of an abortive naval raid by al-Ala against the Sasanian province of
Fars, which ended in heavy Arab losses. In 638–639 Uthman led in person a major assault along the coast of Fars. His brother al-Hakam accompanied him, while he left al-Mughira to oversee administrative affairs in Bahrayn as his deputy. In 639 or 640, Uthman and al-Hakam captured and garrisoned Arab troops in the Fars town of
Tawwaj near the
Persian Gulf coast, southwest of modern
Shiraz. In 641 Uthman established his permanent headquarters at Tawwaj, which he fortified. From Tawwaj in the same year, he captured the city of
Reishahr and killed the Sasanian governor of Fars,
Shahruk. By 642 Uthman subjugated the cities of Jarreh,
Kazerun and al-Nubindjan. About 643, Uthman's forces were joined by
Abu Musa al-Ash'ari, the Muslim governor of
Basra, who had been fighting against the Sasanians on the Iraqi front. Uthman retained overall command and together, they conquered
Arrajan and the area of Shiraz, while Uthman conquered the city of
Darabjird further east without Abu Musa. These conquests occurred between 643 and 644. Umar died in the latter year and was succeeded by
Uthman ibn Affan, who retained Uthman in his post for about six more years. Uthman was unable to capture the Sasanian strongholds of
Istakhr and
Jur (Firuzabad) in mountainous central Fars, which were conquered in 649 by the Muslim governor of Basra,
Abd Allah ibn Amir. In that year, Ibn Amir was given supreme command over the armies of Uthman and Abu Musa in Iran. ==Later life, death and legacy==