Specialist 4 is the 8th of the 24 Puzzles in Subterfuge.
Take control of Vintgar.
You may chose to promote a specialist instead of hiring a new one. Specialists that can be are denoted by a star icon. When you promote a specialist, it is replaced by another specialist with different abilities. As a side note, the red circle around Verne marks the firing range of the sentry.
Try promoting your Sentry instead of hiring a new specialist.
To see the solution click Expand below.
Promote your Sentry to a War Hero, and send all drillers and your War Hero to Vintgar.