Complex sentence: Arriving in South Vietnam, they meet Beckworth whom Kirby allows to join them at the base camp where he witnesses the humanitarian aspect (irrigation ditches, bandages, candy for children) of the Special Forces mission.
Split into simpler sentences: Arriving in South Vietnam, they meet Beckworth, whom Kirby allows to accompany them to the base camp. There, he witnesses the humanitarian aspect (irrigation ditches, bandages, candy for children) of the Special Forces mission.