A siege is a prolonged military assault and blockade[?] on a city or fortress[?] with the intent of conquering by force or attrition[?].
Sieges usually involve surrounding the target and blocking the provision of supplies.
... of the Typhoon to the RAF have begun.
The first unit to form will be an Operational Conversion Unit[?] at RAF Conigsby[?] in 2004.
The Typhoon's combat ...