This shirt has a standard crew neck that never goes out of style, honestly.
US Army Shirt Medium Beige Gen III Cold Weather Undershirt Military Base Layer
What I notice is the crew neck, which has a slight stretch for easy movement.
USMC FROG Flame Resistant Long Sleeve Shirt Brown XL Base Layer Peckham XGO U.S.
A nice feature is the regular fit’s collar, which stays crisp and not loose.