In 1982, AMC was willing to try anything to set their cars apart. That must be why they dumped a new Spirit into the water to prove their car, like any other, will rust in 30 feet of salt water.
American Motors Company was always a company that took chances in the name of innovation. Introducing the 1982 Spirit over images of it rolling off of a dock into the water was certainly one of them. It's questionable how successful this approach was as the next year for the updated Gremlin would be the last.
Most confusing is why they decided they needed to show the Spirit being submerged in the water. According to the ad, they are showing it to make a point. Their cars, the "Tough Americans", come with Ziebart rust proofing and a 5 year rust warranty. Two great selling points for the Spirit, unless you decide to do something foolish like drop it in 30 feet of salt water, in which case, your AMC will rust.