In the chapter "91-Tangos", what does 91-Tango mean exactly? What does Jerry Jaax mean when he says "If you have any tendency to claustrophobia, consider it now."?

The 91-Tangos are Army animal care technicians. As for claustrophobia, this pertains directly to the space suits and protective coverings that will be required apparel in the monkey house. Other red flags that would deter volunteers would be that there was no hazzard pay, and they were not allowed to tell their families what they were doing.