The Flyvefisken-class patrol vessels are warships of the Royal Danish Navy. The class is also known as the Standard Flex 300 or SF300 class. The five vessels sold to the Portuguese Navy are locally referred as Tejo class.

StanFlex is a modular mission payload system used by the Royal Danish Navy. Originally conceived during the 1980s as a way of replacing several classes of minor war vessel with a single class of multi-role ships, the StanFlex system consists of weapons and equipment mounted in standardised containers, which can be loaded into slots on the ships. These containers can be swapped out in a short period of time, allowing the ship to switch between roles when needed. The success of the modular payload system led the Royal Danish Navy to design all new warships with StanFlex slots, and to install slots on older vessels during major refits. By 2012, nine ship classes capable of carrying StanFlex payloads were in service.