Why did NASA choose to splashdown in the Pacific rather than the Atlantic during Apollo?

Answer 1

Though there were several factors, the areas chosen were primarily weather related. Pacific weather is typically a lot calmer than the Atlantic in the areas used for recovery, and most of the Apollo manned-mission dates fell within the Atlantic Hurricane season (June 1 - November 30) or wintertime, making it a risky proposition at best for an Atlantic recovery.

The Apollo capsules, though they could float, needed to have a flotation collar attached by Navy divers prior to Astronaut egress to ensure it wouldn't sink once the hatch was opened. This hard lesson was learned after the hatch on Gus Grissom's Liberty Bell 7 during the Mercury missions blew open prematurely, took on water, and had to be jettisoned by its rescue helo.

For the Apollo missions, rough weather would've made it much more hazardous to recover all 3 of the Astronauts, as well as the cargo (Moon samples) and valuable information in the capsule. Areas were chosen also only after the weather was deemed to be suitable for splashdown.

Most areas in the Atlantic experience 3-5' waves regularly, usually higher. Though the Caribbean is calmer, it's also a lot shallower, and both aircraft and helicopter carriers require deep water to operate.

Answer 2

NASA chose to splashdown in the Pacific Ocean for Apollo missions due to safety considerations. The Pacific provided a wider area for recovery and was less populated, reducing the risk to people on the ground. Additionally, the favorable weather conditions in the Pacific made it a more suitable landing site.