To confirm a doubt lingering in my mind:

Inter-Planetary Missiles will only target stationary defenses, right? Or will they also aim against fleets that are deployed to the planet being targeted?

As well, can IPMs target moons?

And what percentage of defenses, exactly, will be impacted in a strike?

Stationary defense on planets only damage is based on the difference in the launchers Weapons research versus the defenders Armor research.

Oh, I see. Thank you for the immediate reply.

However, I have a new question. If IPMs only target planet-based defenses, exactly how useful are they when they cannot attack fleets, resources, or moons? Are they really worth building expensive silos and then acquiring the missiles themselves?

There's the million dollar question. Everyone's got their own opinion on that one.

IPM's I find are a waste of resources. They have a use when whittling down the defences of an inactive farm perhaps.

For taking out the planetary defences of an active player they are pretty limited, if the defending player can out produce you in mine production and has a greater level of missile silo then the ABM's they can produce means you are just launching for no real reason. Like urinating on a blazing inferno, lol. It will dampen it down a little in places but you will not stop the fire.

I see... I guess we could say that IPMs are most suited as a counterweapon against defense-heavy / turtling players, although with what mightyoz said about ABMs being easier to make than IPMs, it may not be effective even in that sense.

I have made perhaps more heavy use of them than many.

Throughout my time in Standard, I have launched 3,250 of them (actually more, but tracking of these was implemented in Standard some time after I started)

I believe them effective in instances where turtles inactive, or with fleet down several hours, have a rather juicy prize hiding in shells that my fleet cannot penetrate.

Against an active player - particularly one who can replenish ABMs and defenses quickly - they have little utility.