In the 1960s, General Electric and Ralph Mosher built a 3000-pound, quadruped robot dubbed "the Walking Truck." Although the Walking Truck never caught on, you can still check out fantastic footage of this four-legged supply vehicle in motion.
Decades before robots like Big Dog and Quattroped were on the scene, roboticists were researching the practical applications of walking vehicles. In 1962, The Times Record noted that the US Army was looking into a robotic pack beast:
The mechanism for which the Boston Ordinance District has awarded a study contract, would be called a "pedipulator." It would be designed for rough or muddy terrain and its 12-foot legs would hike at 35-mile speed.
The human operator, who would be coupled directly to the mechanism, would walk inside the big machine and the 12-foot legs would take the same steps. The arms of the machine would follow the movements of the operator's arms.
Two or three machines might be lined up like men carrying a stretcher, or a litter, and thus transport equipment or men. The body of the pedipulator would be big enough to hold, besides the operator, electronic circuits, servo units and power drives.
After successful tests of the pedipulator, the military asked GE to build a Cybernetic Anthropomorphous Machine (CAM). Unfortunately for legged automaton aficionados everywhere, the Walking Truck peaked at five miles per hour and proved to be a taxing drive for its operator.
The Empire Strikes Back's vehicle designers didn't explicitly base their designs on Mosher's Walking Truck, but Empire art director Joe Johnston did mention that he drew inspiration from the walking vehicles' 1960s salad days. In 1980, Johnston discussed the AT-AT's origins:
At first they considered using existing military tanks from the Norwegian army, redressing them to make them look alien. I did a bunch of sketches using the tanks as a basis. Then I ran across a xerox that a friend of mine had. It as a promotional brochure put out by U.S. Steel in the early Sixties and contained a whole slew of full-color paintings indicating 'what steel will be used for in the future.' The paintings were done by Syd Meade [sic]. Interestingly enough, one of the paintings showed a four-legged walking truck! That's where the initial walker idea came from. It was a very unique design.
The Walking Truck presently resides at the US Army Transport Museum in Newport News, Virginia. You can learn more about this retro mech and see more fantastic photos at Cybernetic Zoo and David Buckley.