This Guest Post is by Mario McKenna of the Okinawa Karatedo Kitsilano Dojo in Vancouver, British Columbia, Canada. Mario is an instructor of Tou'on-ryu Karatedo and Ryukyu Kobudo. He is the English translator of Kobo Jizai Goshinjutsu Karate Kenpo (Kenwa Mabuni, 1934) and Seipai no Kenkyu Kobo Jizai Karate Kenpo (Kenwa Mabuni, 1934). His article Okinawa Kata Classification: An Historical Overview appears at the Hawaii Karate Seinenkai website. Mario also has an excellent Karate Blog.
The use of the “Kake-goe” is not clearly delineated in Okinawa karate. It seems that the use of the voice to project energy (i.e. kiai) was a part of karate, but not a formal part of training. There are many folk tales of karate fighters who were known to have "given a spirited yell" during a fight. This would suggest to me that it is a natural occurrence, and one that did not need practice during training. Considering that there is / was ample discussion on developing and storing "ki" in the tanden in both modern and classical karate, I would suspect the idea of releasing this energy through the voice would have crept into the discussion.
However, I do not think the use of kiai was a fixed practice. In my own case, when I learned Goju-ryu / Tomari-te, the kiai was at a predetermined fixed point in the kata; no ifs, ands, or buts. However, when I started practicing Tou'on-ryu, Kanzaki sensei simply said to "kiai" at whatever point in the kata I naturally felt like. Or to not "kiai" at all if I felt like it. It was entirely up to me. Nothing written in stone.
I suppose in my own humble view, "kiai" in classical Okinawan karate is simply an option that the student can use or not. It is entirely up to him or her.