.WSA files are animations like the earth globe turning around.

You can't do anything with them but switch them: that gives a funny result.
every .WSA file ends with bytes "80 00 00 80".
.WSA files are also used in DUNE II, but DUNE II WSA's can't be seen in C&C
ans C&C WSA's can't be seen in DUNE II.
In DUNE II they are also used as not-animated pictures.

MIX File:       Size:   Name:           Description:
--------        ----    ----            -----------
GENERAL         130278  GREYERTH.WSA    Turning earth globe (black/white)
GENERAL         151093  E-BWTOCL.WSA    Turning earth globe (bl/wh -> color)
GENERAL         400197  EARTH_E.WSA     Zooming in on Europe
GENERAL         348253  BOSNIA.WSA      Last GDI mission: zoom in on Bosnia
GENERAL         225351  EUROPE.WSA      The conquering of Europe
GENERAL         427648  EARTH_A.WSA     Zooming in on Africa
GENERAL         321867  S_AFRICA.WSA    Last Nod mission: zoom in on S-Africa
GENERAL         173963  AFRICA.WSA      The conquering of Africa
GENERAL         183434  MLTIPLYR.WSA    Multiplayer score screen.
GENERAL         129213  S-GDIIN2.WSA    Win screen build up animation (GDI)
GENERAL         15233   SCRSCN1.WSA     Win screen build up animation (Nod)
TRANSIT         215993  CHOOSE.WSA      The "Select transmission" screen.

Written by Maarten 'Nyerguds' Meuris
http://cnc2sw.planetcnc.gamespy.com/