I'll show you with a couple of pictures.
Here is a picture of a 3 simple tubes. Each is identical except for the smoothing groups.
The first one on the left does not have any smoothing group so you can see the polygons making up the sides.
The second, in the middle has had all the sides assigned to a single smoothing group (you can have many smoothing groups with each group having a different number). The surface normals (which determine how light reflections will be calculated) are averaged over the surface of the polygon and this produces a nice rounded shading effect.
The third, on the right, shows what happens if you make the end caps the same smoothing group as the sides. The result is unrealistic shading as the rendering engine is trying to average surface normals for polygons that meet at 90 degree angles.
On Harry Truman CVN-75 I can see smoothing group artifacts on the sides of the ship. This is easy to spot as there are unnatural patches of light and dark on the sides and those patches are square and triangular in shape (meaning they follow the lines of individual polygons). I have highlighted a few of these spots in the picture below:
You (or your modeler) need to load this model into a modeling program and select groups of polygons and assign them to their own smoothing groups.