Class 3 defensive

From Memory Alpha, the free Star Trek reference

Class 3 defensive was a classification of armaments used on some Federation starships in the 24th century.

In the mid-2360s, the USS Lantree, a class 6 Federation supply ship (a variant of the Miranda-class) was one Federation starship armed with class 3 defensive armaments. When the Lantree sent out a distress call in 2365, it was inferred that these armaments would not be very effective in combat. (TNG: "Unnatural Selection")