Woulda replied this earlier, but the PC is still broke and I spent the weekend being effectively blind with an eye infection.
My interpretation of that was "you can outright hide in space", which to me said "undetected". Unless you handwave out thermal radiation, the best you can do is a ballistic trajectory on minimal power, pretending to be something you're not or lighting up the ECM suite. The last of these can degrade targeting solutions, but it's going to be plainly obvious that something in your general vicinity lit up an ECM suite.
So, if you wanted to do a stealthy insertion into a solar system... you can't, not so long as there's enough sensor platforms to eliminate jump signature blindspots and enough mobile units to check the volume around a jump signature. You can maybe get away with inserting a spec-ops team via piggybacking on an otherwise innocuous ship, using cold-gas thrusters (with very limited dV) for course corrections on an otherwise ballistic trajectory. Even then, the sufficiently paranoid can notice that a freighter was, however briefly, on a ballistic trajectory towards some sensitive installation +/- a few hundred m/s dV, and scramble a mobile unit to scan the volume where a specops team might be.
I treat sensor nodes picking up jump wakes as analgous to Over The Horizon Radars picking up radar contacts at thousdands of KM range, or EO/IR maritime surveillance sats picking up ship wakes. An OTH radar can see
something 3000 km away, but it cannot perform target discrimination (i.e. tell what that something is) and it doesn't have enough resolution to use that blip on the radar for targeting; it needs to cue a sensor asset with faster turnaround time to go and take a look. Likewise with an EO/IR sat that sees a ship's wake: there's a lot of ships wakes out there, at from orbit, a carrier's wake looks a lot like an oil tanker (and they're pretty much the same size, so it's hard to tell them apart unless you have high resolution sensors, which means a much smaller search area since physics mean you have to trade wide angle for zoom focus).
As for ECM... there's lighting up an ECM suite, and then there's lighting up an ECM suite. You're thinking of brute force jamming - to use an analogy, if radar is stretching out hands to feel for something, brute force jamming is punching those hands away. But ECM has advanced beyond that point - sophisticated ECM suites, like the F-35's AN/ASQ-239 (aka Barracuda) and Rafale's SPECTRA use emissions to deflect and weaken the returns of the enemy radar. It's akin to using tai chi to gently redirect those searching hands away. You achieve stealth not by being completely invisible to radar, but being invisible
enough, by lowering your signature enough that the radar return is so weak, it drops below the receiving radar's noise threshold. (As an example: Aegis is sensitive enough to track bird-sized objects. Nobody is going to run it at that level of sensitivity because then the screen is filled with noise, so they set the radar to filter out returns below a certain size.)
Which is a longwinded way of saying that no, if you slip into a system outside of the range/coverage of sensor nodes, running in deception ECM, you
can hide an invasion force. Mind you, this is if you're running
deception jamming, targeted sensor/comms jamming like what TF Soyeon's capships did to FC2-PPV-880652 is deffo going to be picked up, because the jamming is stronger, more concentrated.
While IR and IIR are used on warships, they're not very effective for long range searching due to sensor resolution being a problem (plus, this is where my combat model being 21st century naval warfare. Comes in. I'd say it's about as contrived as the Age of Sail in Space trope.
) IR gives you bearing but not range, IIR needs you to have someone look at an image... these methods become more useful in the close range fight, where they're used along with EO and radar and LIDAR for sensor fusion to defeat ECM.
Like, at the end of the day, this is a politics quest about an empire ruled by foxgirls with fluffy tails. This is
not the quest for hard sci-fi mechanics.
On a side note, I wouldn't be surprised if the Hoou "heavy corvettes" were arranged such that with a bit of dockyard time, components could be re-arranged to free up enough volume for an FTL drive.
Word of God here: not happening. This would basically be on the same level, IRL, as gutting say an Arleigh Burke to swap the gas turbines out for a nuclear reactor.
Could it be done? Sure. Is it
practical to do so? No, because even with modular assembly you still have to cut open the ship, rip out the guts, put the jump drive in and reassemble everything. Like, that's cancerous enough when assembling a PC (god i'm still triggered by all that fruitless troubleshooting), what more a ship. By the time you're done, it would have probably been faster and easier to build a new ship - especially since putting a heavy corvette in for the refit to turn it into a DD takes it off the picket force. (admittedly, this is not really a dealbreaker if it was supposed to be going in for refit anyway, but still.)
"We know there is a force entering the system" and "we know where this force is accurately enough to jump on top of them/shoot them" are not one and the same. (Note how Yui's gank squad arriving in Egon was spotted more or less immediately upon arrival). Plus light-lag exists; unless you're shoving an ansible on every out-system jump detector it'll be a while before you hear of something new arriving.
So, to piggyback on this, if we look back at what happened:
Your three light cruiser squadrons jump into Egon in screening formation, on the very edges of the system, ECM in deception mode, sensors passive, scanning for potential threat. They then do a tactical jump further into the system, within range of Egon's listening posts: first they signal the all clear to your taskforce, and then they drop their ECM and make their presence known. Egon System Traffic Control immediately hails and challenges them, but the Hang Tuah's captain is already playing his role, loudly and publicly proclaiming he's leading an Imperial Navy task group on a Freedom of Navigation exercise, that they don't take their marching orders from Egon STC, that they are on Her Majesty's service and are not to be hindered (and oh, by the way, might they be pointed towards docking berths for a spot of shore leave) -
So from Egon SDF's perspective, Hang Tuah's CL flotilla jumped into the edge of the system, outside of Egon SDF sensor node coverage - because not everybody has seeded sensor nodes/listening posts throughout their systems, then tacjumped closer in and dropped their ECM and went loud, which made Egon SDF shit themsleves. So yes,
@Starman4308 against someone who doesn't have sufficient sensor coverage in the system, you can still make surprise attacks. And plenty of systems have designated shipping lanes for efficient movement of merchant shipping, so it is possible to slip into a shiplane and maskirova (at least, until an inspection boat comes for a looksee).
Which, idk, they might have ansibles but it's been a while since I read the "how to war in Space Foxes Quest" post and I don't think it mentioned early-warning nets much anyhow
I have no idea what ansibles are - my paradigm for FTL comms is based on my experience growing up in the jungle.
Tl;dr FTL comms move 10 times the speed of FTL travel, so there's a 4-hour transmission lag between Egon and Jinko Sei (which is also a 4-day travel time by ship), and you have FTL comm bouys analogous to radio retransmission stations that are relaying signals from system to system. (And now I am reminded of when, growing up in the jungle with an ATUR phone, we had to drive up the hill to get signal for incoming and outgoing calls. Goddamn that thing was heavy.)