City of London, launched in 1800 as an East Indiaman, made six voyages for the British East India Company between 1800 and 1814.
On April 14, 1804, the ship, with Captain Abraham Green in command, obtained a letter of marque, and sailed from Torbay on May 27 for Bengal and Madras.
It reached Calcutta on December 6. A letter of marque was a licence issued by a nation that allowed a private individual, or a ship, a “privateer”, to take part in war or be used as a ship of war and attack and capture ships of a nation in conflict with the issuer of the licence.
Before navies were established, European nations, and later, the US, tended to depend on private ships considerably in their war efforts.
Admiralty courts were established in England to judge the cases of captures made by privateers. In 1856, privateering was banned by the Declaration of Paris, but the US continued the practice, which was also less expensive for a nation, as it did not have to pay privateers. But often it was impossible to keep privateers within the bounds of the terms of the letter of marque.
City of London arrived in Calcutta on December 6, 1804. It would sail for a few more years, till it was broken up.