This film was about as stupid as the first one was intelligent.

If it came out now it would win picture of the year.

I'm afraid it still doesn't make sense. Taylor's ship "disappeared" in the sense that the radio transmission that he was supposed to send to earth never got sent after the ship crashed (the water flooding the craft killed the ship's power supply), but that happened more than 2,000 years after the ship was launched. The 20th century United States would have no possible way of knowing this. Once the ship reached a speed close to that of light, relativistic time dilation meant that centuries pass on earth for every month they spend in space. The ship would quickly reach a point where the 1960s/70s U.S. could have no way at all of knowing what happened to the ship and crew, whether they reached their destination safely, hit something on route and were destroyed, crashed into the planet, exploded because of a malfunctioning reactor, or were wiped out of existence by the hand of God Himself. They just couldn't know. Hence, there is no conceivable rationale for a "rescue mission."

The reality is that this, as well as Cornelius and Zira and Dr. Milo, somehow salvaged Taylor's (or Brent's) ship, and traveled backward in time to 1970s Earth (despite the apes apparently having no better than a late-19th century technology, and shouldn't be able to understand something as complex as an interstellar spacecraft and how to fly and navigate it), are serious plot holes. They are just handwaves to allow the studio to squeeze out sequels to as unexpectedly very successful movie that was clearly meant to be a stand alone film, and was never meant to have sequels at all.

Thank you, TJLamb. I agree they all had their flaws. To me, these are the quintessential popcorn movies. They are just so much fun, I forget all my critical thinking skills and have a little fun.