This article needs additional citations for verification. (January 2013) (Learn how and when to remove this template message)
An aviso (Portuguese and Spanish term for "advice", "notice" or "warning", formerly also an adviso) was originally a kind of dispatch boat or "advice boat". The term was later adopted by the French and Portuguese navies to classify their medium-sized warships designed for colonial service. The term continued to be used in the French Navy to classify the D'Estienne d'Orves–class patrol frigates until 2012, when the remaining ships of the class were reclassified as offshore patrol ships. It is similar to the modern use of "sloop" in other countries.
The Dictionnaire de la Marine Française 1788–1792 (by Nicolas-Charles Romme) describes avisos as "small boats designed to carry orders or dispatches". This use became obsolete with the development of means of communicating detailed information at a distance.
French World War I avisos, used also during World War II, had displacement 300–700 tons, speeds of 13–20 knots, main armaments usually of two 100 mm guns, two 138 mm guns, or four 100 mm guns. Colonial avisos, such as the Bougainville-class aviso intended for overseas service, were larger.
The Portuguese Navy used avisos to operate in the waters of the Portuguese Empire. The Portuguese built 1st rate avisos (Afonso de Albuquerque class) of 2,400 tons and 2nd rate avisos (Gonçalo Velho and Pedro Nunes classes) of 1,200 to 1,700 tons. In 1932, the Portuguese Flower-class sloops were also classified as 2nd rate avisos.
The term is now used to include combat-capable ships larger than patrol boats, but smaller than corvettes. They typically have roles in anti-submarine warfare and coastal defence. In NATO classification they are usually recognized as corvettes.
The Argentine Navy has several ships classified as avisos. ARA Alférez Sobral, an 800-ton aviso used for non-combat tasks, built as a US Navy fleet tug, was attacked and damaged during the 1982 Falklands War.