This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
Until the 1979 Pink Book revision, different power classes
were designated by names. For gliders, the names were of
flying creatures. Here is a decoder table:
1/8A [none] 1/4A Gnat 1/2A Hornet A Sparrow B Swift C Hawk D [no official name. The "Pink Book" used to lump D and E into one category. Sometimes called Deagle or Falcon ] E Eagle F Condor G [no official name. This class did not exist back when names were used, but was occasionally referenced as Dragon]