McCampbell UFO Vehicle Classification System

The primary UFO types appear to be:

Spheres and discs between 1- and 3-ft diameter that are almost certainly sensing devices, either preprogrammed or remotely controlled. They have been seen to emerge from standard craft, fly around for extended periods, then return for pick up. The kind of measurements that they take can only be guessed. 

Three principal types eventually belong to this group; 

a) An egg-shaped machine about 6- to 8-ft long that flies with the long axis vertical, comparable in size to a compact sedan. 

b) An elongated cylinder without external appendages that flies in the direction of its axis, comparable in size to the body of a jet fighter. 

c) A spherical object about 15 ft in diameter.

This group, accounting for about half the sightings is dominated by the basic disc with numerous variations. Most common size is about 25-  to 35-ft diameter. 

Several different types. Most frequently reported is a disc about 100 ft diameter. An even larger one, several stories tall inside, probably has a diameter between 250- and 300-ft. A large cigar-shaped craft should also be included here. 

Seen only at very high altitude is a gigantic, cigar-shaped machine that is probably twice as large as an aircraft carrier and, perhaps, as much as 1 mile in length. Smaller craft have been seen to be discharged from them in large numbers. 

The Vehicles - Complete Chapter 2, UFOLOGY McCampbell
 NICAP Home Page