The throngs of New Yorkers who poured into Coney Island on a sweltering Sunday in July 1939 — shuffling past the rides, hot dog stands and freak shows — confronted one last spectacle blaring just beyond the surf.

At 65 feet and outfitted with enormous Trump signs, the yacht called the Trump Show Boat was hard to miss. And that was the point.

Its loudspeakers blasted recordings of “The Star-Spangled Banner” and “God Bless America” over and over, compelling many sunbathers, reluctant to be seen as unpatriotic, to stand and salute each time. When the boat floated swordfish-shaped balloons — redeemable for $25 or $250 toward a new Trump Home — toward the shore, bathers nearly rioted as they raced to snatch them up.

Fred C. Trump, the owner of the boat and the master builder of solid homes in Brooklyn and Queens, is often considered a point of contrast to his flashy son Donald, the brash developer who built gilded towers in Manhattan, and became a tabloid fixture, television personality and now, Republican presidential nominee.