I got a question for you: In 1971, research chemist Stephanie Kwolek discovered a liquid crystalline polymer solution. Its exceptional strength and stiffness led to the invention of Kevlar ®️, a synthetic fibre, woven into a fabric and layered, that, by weight, has five times the tensile strength of steel. In the mid-1970s, DuPont the company which employed Kwolek introduced Kevlar. Immediately Kevlar was incorporated into a National Institute of Justice (NIJ) evaluation program to provide lightweight, able body armor to a test pool of American law enforcement officers to ascertain if everyday able wearing was possible. Lester Shubin, a program manager at the NIJ, managed this law enforcement feasibility study within a few selected large police agencies, and quickly determined that Kevlar body armor could be comfortably worn by police daily, and would save lives.

Answer this question: when was kevlar first used as body armor?
Let's think first:
The important part for answering this question is: Immediately Kevlar was incorporated into a National Institute of Justice (NIJ) evaluation program to provide lightweight, able body armor to a test pool of American law enforcement officers to ascertain if everyday able wearing was possible.
Therefore, the answer is In the mid-1970s.