They cost $25,000 each to build, and were meant to be a little cool-off center for underserved neighborhoods. They traveled all over the five boroughs, and were easy to transport. In just a few years, by 1972, there were 72 of them.
Then, during the Heckscher administration, swimmobiles were introduced. While the portable pools were phased out with the addition of more permanent structures, these seemed to last into the 1980s. In 1987, the NY Times spoke to 12-year-old William Ricks in Brooklyn, who was enjoying a new swimmobile—he told the paper, "My friend Raymond isn't here today, and he'll never, ever believe this. It's like a U.F.O." The trucks would be parked in the streets all day, before rolling back out at night.
While the Parks Department hasn't answered our inquiry about the possibility of the swimmobiles returning, a few years ago some luxury dumpster pools surfaced as part of the DOT's Summer Streets initiative.