The four-legged, gyro-balanced, walking cargo vehicle shown on pages 80-81 is from the US Steel Interface portfolio series [published in 1969 - see image below]. The environment is arctic and the mission is to deliver goods and critical supplies to an isolated exploratory colony beyond the DEWline. Like several of the preceding designs, the 'feet' can be rotated and locked to form powered wheels for rolling over smooth terrain but, seen here in the walking mode, they are covered with ice that is breaking up into radial slivers as the pneumatic pods flex. Defining this part of the design concept more closely, Mead explains that "the largest land animal now extant is the elephant. As he puts his weight on each foot the metacarpals and tarsals fan out from the ankle and the foot spreads, distributing the pressure. Conversely, as the weight is retracted the foot contracts and never gets stuck in the mud. The same principle was incorporated here; the 'foot' structure would be alternately inflated and deflated in the walking mode to duplicate the natural function of the elephant's foot. As a matter of fact, when I did this the US Government had already funded a military project for a walking machine [RH-2010 - the GE Walking Truck] and had built an analog computer-co-ordinated prototype that successfully walked over loosely stacked railroad ties. The seated driver not only operated extremely sensitive hand and foot controls that duplicated and amplified his motions, but also had calculated feedback that allowed him to 'feel' the feet making ground contact!"