The Persian Gulf campaign of 1809 was an operation by the British East India Company and Royal Navy to force the Al Qasimi (plural Qawasim, referred to by the British at the time as 'Joasmees') to cease their attacks on British ships in the Persian Gulf, particularly on the Persian and Arab coasts of the Strait of Hormuz. The operation's success was limited as the British did not press their advantage when invading Ras Al Khaimah and embarked without consolidating their gains and failed to permanently suppress the strong fleets of the Qawasim of Ras Al Khaimah and Sharjah. The expedition did achieve its short-term goals by destroying three Al Qasimi bases and over 80 vessels, including the largest Al Qasimi ship in the region, the converted merchant ship Minerva. Although operations continued into 1810, the British were unable to destroy every Al Qasimi vessel. By 1811, attacks had resumed, although at a lower intensity than previously.

The operation against the Qawasim was a joint campaign by the Royal Navy and the fleet of the Honourable East India Company (HEIC), with soldiers drawn from the garrison of Bombay. The expeditionary force, led by Captain John Wainwright in the Navy frigate HMS Chiffonne, was despatched to the region, following an escalation in attacks on British shipping in the Persian Gulf after the French established diplomatic missions in Muscat and Tehran in 1807. These attacks not only threatened British trade links in the region, but also placed British relations with Oman and Persia in jeopardy at a time when French aspirations against British India were a cause for concern to the British government.

Because the available charts of the Persian Gulf were inaccurate or incomplete at the time, Al Qasimi ships could hide from Wainwright's squadron in the uncharted inlets, a problem Wainwright reported upon his return that resulted in improved British cartography of the area.

In the early 19th century, the Indian Ocean was an important link in the trade routes from British India to the United Kingdom, and Honourable East India Company (HEIC) merchant ships, known as East Indiamen, regularly crossed the ocean carrying millions of pounds worth of goods. One of the most important ports for the Indian trade was Bombay, on the western coast of the Indian subcontinent, a significant hub for regional trade with its links to the Persian and Arab ports of the Persian Gulf. The ships that traded in the Persian Gulf were named "country ships" and were much smaller and weaker than the big East Indiamen. The British had long maintained a naval presence in the region, but the outbreak of the Napoleonic Wars in 1803 diverted much of the British strength in the Indian Ocean to the Dutch colonies of the Cape of Good Hope and Java and the French bases on Île Bonaparte and Île de France, leaving the Persian Gulf and Arabian Sea largely undefended. In addition, convoy guardships were needed to escort the East Indiamen through hostile waters and the Navy presence in the Gulf was replaced by warships belonging to the "Bombay Marine", the HEIC's naval arm.

The vessels of the Bombay Marine were spread across many thousands of miles of ocean, often leaving the country ships in the Arabian Gulf undefended. As French raiders were rare in the Gulf, few country ships operated in convoys and so they became targets for dhows and bhagalas operating from semi or completely independent harbours in Persia or along the Arabian Peninsula.

The Qawasim, a federation of tribes spanning Sharjah, Ras Al Khaimah, Qeshm and Luft, were the dominant local force and in alliance with the Omani Imam but at war with the Sultan of Muscat who had been a British ally since 1798. Omani ships from both sides cruised the Gulf and those allied to the deposed Imam felt free to attack the ships of their enemy’s ally: the British.

In 1805, the Qawasim captured two large ships, Shannon and Trimmer; the small boats of the Qawasim swarmed the larger merchant ships and massacred the crews. The Qawasim converted Trimmer into a formidable pirate ship. When the warship HCS Mornington, which carried 24 guns and carronades, attempted to recapture Trimmer a few months later, nearly 40 Al Qasimi vessels attacked Mornington, which only just managed to escape destruction herself.

Lacking the available naval forces to launch a sizeable campaign in the Gulf, the British authorities attempted to use diplomacy to end the threat. In February 1806, the young Sultan of Oman, Sa'id II ibn Sultan, signed a treaty at Bandar Abbas promising to bring an end to attacks originating from his territory, but by 1807 the French had installed consulates in Tehran and Muscat and attacks continued unabated with their encouragement. In 1807, Lord Minto, Governor General of India, determined to send ambassadors to the Sikh Empire, Afghanistan and Persia in an effort to secure their support and prevent the French from gaining allies on India's western borders. As part of this diplomatic campaign, the ambassador to Persia was instructed to discuss the problem with the Persian government, but due to French influence in Tehran, he was unable to obtain any guarantees.