Flush with victory over two advanced alien vessels, whom I suspect to be Precursors, with only minor losses, after rearming and replacing losses, I brought two fleets totaling 12 ships total, more than half my navy, back into the system to clear the inner system. What I ran into was a threat wholely unlike that which I had previously faced.
The first two vessels I fought, outranged me but attacked singly. They hit from well outside the range of my fire control, packed a bit of a whallop at size 13 nuclear detonations and moved so fast and were so stealthy that my area defense ships could not even get a radar lock, I picked them up on thermals only. However, they only fired volleys of four and my CIWS was generally good for a missile, sometimes two if I was lucky. Early on I fired off about 75% of my missile stocks at a waypoint between us, not sure what to expect and wanting my missiles to be of some use before I was turned into floating wreckage. What I hadn't anticipated was that the first alien ship ran out of ammo after only managing to kill one ship.
I was thus able to push on to engage within my own fire control ranges and gradually wear him down. A second, much larger ship (15 KT) took notice and moved in after I nuked the first alien. He fired off a few volleys of the same high speed missile that I could only track on thermals but shot himself dry after just a handful of salvos. He then rammed one of my heavier ships, destroying himself and it.
With more confidence in my ability to handle these aliens, I sent back the first fleet to rearm and reinforce and brought a second with it. We pushed on into the inner system and discovered a pair of what I believe to be PDCs on an inner planet. Instead of small volleys of very large, very powerful but manageable missiles: the PDCs sent a hurricane of 56 missiles my way every 10 seconds from just outside the endurance range of my missiles. Like the heavier missiles, my anti-missile missiles were useless, unable to lock on with radar and while CIWS might swat down 2, even 3 missiles out of the storm. 50+ missiles did bad things to my fleet.
Definitely designing a task force leader with the ability to launch probes from safety.