My series of posts have tried to wake up merchants and other spacers to the colorful travellers and phenomena of the space lanes. Mind the colorful people are usually pirates and barbarians and the phenomena you could usually do without. Sorry, those are the thought that come to me out of the ether. I just get custody of them, as George Carlin once said (I'd love to say I wrote this during a lightning storm with a bottle of Scotch in my hand but alas it's a sunny day and I'm sipping iced tea.)
Anyway besides your basic pirates there's another group out there to worry about. They are every bit as relentless (maybe more), they have better technology, they have excellent crews. The Polity Navy takes a dim view of them many times. I refer to the Patrol (with a nod to Lady Andre Norton of course).
There is no branch called the Patrol in most Polities but it's there. Politics indicates a Polity will field fleets to prevent invasion, and rebellion. These fleets will have the most powerful ships and weapons available as well as the highest technology level.
These fleets will be idle and trying to look busy 99% of the time. It's that other 1% that you keep them around for: war, blockades, rebellions, invasions, and spitting on the GHU-Emperor's statue. For fighting pirates these fleets are almost 100% useless. In building big ships to serve as deterrents you are concentrating your forces. Fighting a group of pirates or a smuggling fleet with a fleet like this is much like taking a sledgehammer to a swarm of gnats. The pirates go where the big ship[s aren't. Big ships require a scheduled route for political and defense considerations. This may be the same thing. Fleet Day may come early if your Planetary Baron is feeling uppity. Pray they leave early too.
Add to this that a remote central government probably doesn't give a chinchilla's ass about your local concerns or the distress call of that lousy 200 ton free trader ... Roland, Siegfried? I forget the name.
After paying their share of taxes for the Polity fleet member worlds with any sort of leaderships will tighten their belts and pay another tax for their local fleet, usually referred to as the Patrol. Yes it is part of the Navy, much as some regard the Marines as part of the US Navy. You try telling A Marine that and I'll take pictures. Apart from a temporary alliance the Patrol and the Fleet do not work that closely. While the Fleet exists to protect the Polity, the Patrol takes care of things on a local level.
The frontier navy does not have the budget of the Fleet. Small ships are used with local technology that do not require special bases or technicians to maintain. Crew are small. There's no Marine equivalent, ship troops handle boarding actions. Ship's boats are used extensively to augment firepower in a sort of mini-battlerider strategy. These ships are crucial in raiding pirate bases that traditionally have landing fields that are a nightmare for large ships.
The Patrol has relatively small ships (800 tons and under and darned few 800 ton ships). They do try to be everywhere. They use technology locally available and are built for lengthy patrols. Finally the Patrol skipper has a high degree of autonomy. Beyond a few scheduled stopovers for various concerns a Patrol skipper has a group of star system they patrol in whatever fashion they choose, barring orders from above.
The autonomy part gives pirates the fits. The Fleet makes a show of arriving and leaving and goes for shock and awe. It's like a marching band. The Patrol shows up where and when you least expect it, much like the guy who steps on a subway train, starts p[laying a flute and passes the hat around.
There's a difference in culture as well. Navy officers (and crew where possible) will often be stationed in ships and fleets far from their homeworlds. Their first loyalties and interests are to the Polity, not some locals (barring shore leave.) The crew of the Patrol are the locals. The Fleet regards anti-piracy missions as search and destroy missions (usually against a base or a lone ship with phenomenally bad luck/judgement). The Patrol uses local contacts and local rumor mills to ferret out the informants ad fences so necessary for successful pirate enterprises. There are even instances of one pirate ring informing on another group invading their territory to the Patrol. After all locals look out for each other.
The Parol is also relentless in mounting sting operations often using upgunned merchant ships or captured pirate vessels. These stings extend to Patrol crew operating undercover in starports to report suspicious goings on. Besides their own contacts and agents the Patrol cultivates good relations with the Scouts and the Free Traders. Both are valuable sources of information on local shipping. In the case of the traders some helpful tips might lead to the Patrol looking the other way when you have some duty free cargo in your hold.
The system is not perfect. For one thing in some areas the Patrol amounts to a private navy beholding only to its homeworld and little else. In Polities that are confederations local navies may be dominant. These look to their own world leaders and admiralty for orders first then the Polity. The central government usually takes a dime view of this and restricts ship size and armament when it can.
Even so Patrols are often scenes of power struggles as local commanders do not always cooperate with others in a cluster funded navy. It gets worse if one or more worlds rebels against the Polity. In the case of a rebellion the Patrol is usually the first to get the ax. The Polity Fleet will regard them as possibly disloyal and move to disarm them and intern their ships. Similarly some local planets may regard them as tainted by offworld contacts and interests and move to eliminate their officers at the very least.
In a final sign that the Universe's most fundamental force is irony many Patrol ships faced with their homeworld turning rebel turn pirate.