The earliest is the Looky Fire Truck from 1950-1954, so named because of its anthropomorphic face made from the bumper and headlights. Measuring 12 inches long, it came with 3 permanently attached round headed firemen, precursors of the famous Fisher Price Little People.
All the fire trucks had lots of action features. As this one is pulled, the bell clangs; Looky's eyes move as if he's searching for the fire, or perhaps watching for pedestrians; and the two firemen holding on in the back spin around and bob up and down. This early in the Little People evolution, they are only heads, as can be seen below:
The truck is beautifully lithographed in rich colors with lots of details, including ladders, axes, oxygen tanks, hose connections, and gauges.
Looky was followed by the Winky Blinky Fire Truck, made from 1954-1960. The two toys were very similar, but Winky had all new graphics with a cutesier truck face. The firemen and action features were the same, but included the addition of a (non-working) wooden siren.
A radical redesign arrived in 1960 with the introduction of the Snorky Fire Truck. Made for only 1 year, the 15 inch long truck is much sought for its firemen, now full bodied. They, along with their dog, represent some of the earliest iterations of what would become the Fisher Price Little People.
Snorky is a no nonsense fire truck: gone are the goofy headlight-and-bumper face and the merrily bouncing firemen in the back. Instead, it features a real hook and ladder which can be raised, and the firemen can hold the hose in their attached plastic arms.
The Snorky dog is one of the very rarest of Fisher Price figures. He may look odd lacking ears, but that's how he was originally made.
The next and final model of the Snorky was also made for only one year, in 1961. It featured updated lithography resembling more modern fire trucks, but for some inexplicable reason, it didn't come with a dog.
The Snorky Fire Trucks, with their single-year production runs, crankable ladders, and fragile-armed firemen, are some of the rarest, priciest, and most sought after vintage Fisher Price playsets. If you ever spot one of the firemen (or, even more impossibly, the dog) while yard saling, snatch it up: it's a treasure!