Barry discovered that there was a variant of the “4-in-1 Jeep” campaign that used the term “4-Purpose Jeep”. It appears the term only appeared in newspaper ads (I have not extensively confirmed this). Here are some examples.
From the May 19, 1946, issue of the Beatrice Daily Sun Newspaper (Beatrice, Nebraska):
From the June 12, 1946, Issue of the South Alabamian (Jackson, Alabama):
From the May 12, 1948, issue of the Belleville News-Democrat (Belleville, Illinois):
From the May 03, 1951, issue of the Valentine Newspaper (Valentine, Nebraska):
THE 4 – PURPOSES OF A JEEP — TO RUST — TO LEAK BODILY FLUIDS — TO MOVE DANGEROUSLY SLOW OF MODERN ROADS — AND TO CRAWL OVER AREAS I’M UNABLE TO NAVIGATE — NEAL JUNG