What is unique about the tig welding process?

I wouldn't call TIG unique as it was developed to replace Oxy-Acetylene welding. Basically you use a heat source to melt the base metal and either fuse or add filler to complete the weld. TIG, originally called Heliarc (Helium - electric arc), was developed sometime around WWII to weld Aluminum. Helium was used to protect the molten puddle. Since then Argon has become the primary gas sometimes mixed with Helium. Almost any type of metal can be welded with the TIG process. Except for fuse welding it is a two handed operation whereas MIG and stick welding can be performed single handed. One thing that is unique is that with the addition of a foot pedal you can control the Amperage as you weld.

many planes were produced here at Wright with gas welded Aluminum

most was done with Hydrogen Oxygen torch taking care to have a reducing flame