Well, O'l Wally Byam liked boating. I think he envisioned his Airstreams like yachts on land seeking new worlds.
By the 1960s the base trim level was called Land Yacht. My 66 Trade Wind (another seaman's term) has the Land Yacht trim. The more expensive trim was called International. They had special badging, accessories and luxury appointments. I have an
1966 Airstream brochure that explains these differences.
I'm no Airstream historian, but his is my understanding.
David