How often does this happen...?

In order: not very, yes, and not that I know of from the position you were in.

I've only ever had to go up against a Precursor Ranger once, and it was found by a civilization (the Drengin) who only had one planet left. I conquered it, and while the Ranger went pirate it eventually just disappeared without causing much harm - a shame, actually, as one of my allies had found another and I had bought it to try and hunt the pirate Ranger down.

At any rate, the best way I can think of to deal with one is along these lines: don't fight it directly.

Also, while not a common event, it's not a Mega Event and can't be prevented by disabling them.

I'm not sure I've ever encountered the Precursor Ranger in 4 years of playing this game on and off, certainly not in the hands of the AI, so I don't think it's all that common (although different players seem to encounter different events more or less frequently). The player can get them too I think, again quite rarely, I think I have seen it mentioned in forum posts in the past.

To defend against it - if you can convince the Terrans to make peace and then dig in and research for a while, you may in a while be able to swarm it with ships that overwhelm it eventually - and if you bribe someone else to attack them they'll probably send the ship off and you may never see it again (especially if this stronger version is still slow, as I remember the weaker Lucky Rangers being). Usually if I encounter one of the events where there's a vastly powerful new opponent (have you encountered the Mega Pirates or Peacekeepers yet?) this is what I have to do, until I can build ships that can fight back.

You should avoid attacking this warmachine head on until you can actually beat it. Till then, I advise researching Planetary Invasion (if you haven't already) and going on the counter offensive. Ignore the Precursor Ranger, send your ships in to clear enemy planets of their orbital defenders and land your troops on the ground. You should be able to conquer more planets than you lose, and you can even do the same to planets you lost as soon as the enemy ship goes out of range. Don't be afraid to enter a ground warfare slugfest, it is the best way to beat a superior opponent.

If you really insist on taking out this ship, make sure you have built the building that allows all your ships at a planet to defend it together and throw its orbit full with your best ships. Then get the enemy to attack it (defending a planet gives a boost and you don't need to bother with logistics). Right now it seems pretty pointless to try this though.

Space superiority is not necessary to win in GalCiv2 (though it helps), all you really need is the capacity to take out a single defender on a hostile planet, quickly land your troops and conquer planets faster than your opponent... Bringing in a second target for your opponent (as the person above suggested) can be very helpful too, especially since they might clear some enemy planets of hostile ships that you can then conquer with your transports!

As for the frequency: this is (in my experience) a pretty rare event. However, if during your game a single ranger class ship is found, it often happens more will follow! (As you experienced in this particular game.)

Good luck!

My last game, the AI received FIVE Precursor Rangers, the Yor got two of them and the others were traded around until finally I bought three of them.

Usually of course, it's given to the races which are lagging behind badly on Military.

The best way to "defeat" them is to send them off on wild goose chases with ships that can handily outrun them, while also using fast transports to beat the enemy's defenses to their planets.

I know the lucky rangers can't happen in the first 3-5 years, and I was under the impresion the precursor rangers were similarly limited, so there is at least a grace period before they show up, which is generally sufficient, even in TA, to come up with some way of dealing with them, although it can still be painful dependent on your settings (low planet count and slow research will make it harder).

My enemies do get the Precursor Ranger rarely. Most of the time, I manage to obtain them one way or another.

All in all, only three of my games did the enemy kept the ship. And in all three times, they blew up.

One time is when the Peacekeepers showed up and their Precursor Ranger went down in a hurry.

The second time, I manage to catch it alone and, since it is nearly the end of the game with late-game technologies, I manage to crush it with my Revenge Fleet!

The third time, it was in a fleet. But since my Industrial Output was far superior, I built several fleets of 6 battleships that was heavily armed and shielded and sent them against the enemy, They did win against the Precursor Ranger, even with losses.

I've had it a few times, and it do look like it are given to the race that are lagging behind on military might. In one game I was still without a war ship - but far in front in the research department and money wise, the Yor declaired war on me, when I didn't felt like giving out one of my planets, got the ship and steamrolled them, and then also started producing the biggest possible ships with max mini thingy full of black hole guns, against their small +8 attack ship. Lovely

Not always though. During my previous game, the Krynn, who controlled 80% of the galaxy and had a military at least 5 times the remaining two races combined (the Altarians and my hamstrung Yor) received not one, but two precursor rangers, the Alterians received nothing and I received two crappy Lucky Rangers (that came nowhere near the PreCursor Ship) before eventually receiving my own PreCursor Ranger (which was then swiftly blown up because by then its lead on the rest of the galaxy wasn't that impressive).

I didn't mind though. It greatly added to the general feel of the game (OMG I'm gonna die against this ultimate enemy!), and made the end even more of a climactic turn-around. ^^

My strategy when this occurs is a very simple, very effective one. Contact the empire which received UltraMegaSupaship, and BUY THAT MONSTER works every time

I've had precursor corvettes and the precursor rangers and have been on the recieveing end as well.I've conquered entire galaxies with a ranger and had my entire armada wiped out by one solitary ranger.The AI tend to get rid of their Rangers especially if their draining their coffers their on easier settings.

Whenever the enemy gets a ship like this that you simply cannot beat, you have to find a workaround. Straight up buying it is a bit too gamey for me, but avoiding it in combat and opening more fronts of warfare can do the job.

I normally get 1-2 fleets of precursor corvettes per game and as for Rangers can range from none to each race having loads each.I once played a "normal" game against 9 opponents and got my arse handed to me as all the other races got 3-5 rangers each and used them to wipe my empire of the map.

I don't think I've ever received a precursor "corvette"... Didn't know they existed actually!

Contrary to popular belief, you don't need a proper armada to win through conquest

Another tactic involves speed.

As one commenter said, if you get the enemy chasing one target, just lead it off and around and around.  Just take care not to get more than two extra squares away or else it might reset its target.

If the enemy sends transports in its wake, you need faster ships with just enough attack/defense to pick off the transports as they come.  This is similar to how one can deal with the DreadLords, buying time. If the AI embeds the transports in decent fleets, then you have another problem.  There is an exploit to deal with even that, but it is too gamey to be shared in polite company.

All you need is to be able to build a ship or several ships combined, that can take on the more weakly defended planets, then touch down transports. your ships only need to last for their suicide strike for you to still be able to conquer the more powerful enemy faster than he can conquer you. The simple reason for this is AI undervalueing of building transports and carrying out invasions, meaning you can almost always beat it at the planetary combat game. Having good soldiering tech really helps this tactic. If tech stealing is enabled, you can also quickly catch up technologically through this method!

HighWater is correct, and the suicidal deepstrike is fun, especially at Suicidal when the AI has all the other cards.

One can, for example, sort through the enemy planets to find where they have things like the soldier training bonus facility, the aphrodisiac trade good, the eco capitol, etc and target them specifically.  If one spots re-invasion transports in-bound that cannot be stopped, one can raze the bonus facilities or even destroy the entire colony - - relegating it to a PQ 0 planet.

I have yet to test if, once a bonus facility is destroyed in the above fashion, if I can now build it myself within my empire (like the soldier training one).  I think I have done it, but cannot now recall for sure.

It allows a bit of scope for role-playing.

Remember, also, that the first step is taking out the enemy anomaly mining bases!

In DA, the MCC is a conundrum.  It gives a 100% eco bonus, so you do NOT want the enemy to have it.  OTOH, if stops planet-flipping (a known DA bug).  One "solution" I have adopted is to take it away from an AI, let my treasury build, evacuate the planet down to 1 colonist unit, then gift it to another AI, preferably an ally or a minor.  The low population makes the game engine value the planet low, so I can always buy it back with tech later if I need a fresh cash infusion but, in the meanwhile, I flip some more planets.

Thamgere last time I had Precursor corvettes never had ran.gers in the sandbox game I outgunned it and upgraded it,  but this should have the same stratedgy as the dread lords build a heavily armed starbase by their home planet. If U have to bait it a transport paeked at the starbase by their home planet should do the trick. I have had an attack of148 in the past that would outgunn it

Bribe someone else to war against the Terran.