The Patrol Craft stands as a nation's last - and in some cases first - line of defense.
Patrol elements are called upon to defend offshore areas of importnace from enemy incursion. During peacetime, this may include interception of illegal drugs while, during wartime, this would include defense of critical waterways and offshore positions that threaten vital shipping lanes. Large patrol forces are common with those powers seeing relatively limited naval budgets.
For the purposes of the GFP ranking, Patrol Craft include various weight classes such as coastal/'Blue Water' and missile/torpedo boats. LAs stated elsewhere on this site, landlocked nations are NOT penalized for the lack of a standing naval force though nations with a standing navy ARE penalized for lack of certain naval assets.