A class-2 probe was a type of probe carried aboard Federation starships, including Danube-class and Galaxy-class vessels.
In 2366 the USS Enterprise-D launched a class-2 probe loaded with Hytritium to combat a tricyanate contamination of the water supply on Beta Agni II. (TNG: "The Most Toys")
In 2369, Benjamin Sisko proposed using a class-2 probe to investigate a narrow band subspace signal emanating from a moon in the Gamma Quadrant. (DS9: "Battle Lines")