'Night Intruder' ???

[Wiedrock]

Night Fighters cannot usually be directly assigned to
AS missions if they fly at night. The exception to this is
if they are allocated to the ‘night intruder’ mission and
ordered to target airbases where enemy night bombers or
fighters may be based. Instead Night Fighters rely on auto-
interception to engage with enemy air missions.

What does it mean, what is it for and how and why to use whatever it is?

[Denniss]

I suspect a leftover from WitW

[Joel Billings]

Not sure if it's still in WitE2, but IIRC you could launch a strike against an airbase including the night fighters and they would go and attacking night aircraft operating from there, but I could be remembering this incorrectly.