Newt is Britain's best kept secret of WW I. Even his brother Theseus believes that Newt simply was in a work-related accident that very nearly killed him, not that he is the unspeakable that saved a lot of lives with dragons no less. So it's understandable when british and american aurors, Theseus, Graves and Tina included, are in a tight spot against Grindelwald's forces and suddenly Theseus' precious little brother enters the scene saving everyone again.

Bonus for Newt still being his shy, awkward self.
Double Bonus for Theseus begging Graves to keep an eye on Newt when they have to leave on seperate missions because he still remembers in vivid detail how close to death he came the last time.
Triple bonus for Newt being an animagus...a tiny owl that's so unassuming that noone thinks it could be a threat. That's one reason he becomes one of the scouts for missions.