Complex sentence: Taking on enemy tanks were the job of purpose-built tank destroyers, and the wide array of special duties that a tank could be used for were just being explored by armies around the world in the early 1940s.
Split into simpler sentences: Taking on enemy tanks were the job of purpose-built tank destroyers. The wide array of special duties that a tank could be used for were just being explored by armies around the world in the early 1940s.