Complex sentence: While at Bletchley Park, he supplied the Soviets with advance intelligence from ULTRA about Operation Citadel, and in particular the Battle of Kursk, the world's largest tank battle, which set the seal on final defeat for the Wehrmacht in the East.
Split into simpler sentences: While at Bletchley Park, he supplied the Soviets with advance intelligence from ULTRA about Operation Citadel. This led to the Battle of Kursk, the world's largest tank battle, which set the seal on final defeat for the Wehrmacht in the East.