The first modern ultrasound transducers that were utilized were single-element probes. These probes had a fixed depth that they were able to reach, which varied based on the engineering of the specific unit.
Ultrasound machines have come a long way. The first ultrasound machine was a 2D scanner debuted in 1958 by Ian Donald and Tom brown. They called it the Diasonograph, but it was known in more informal and unkind circles as the Dinosaurograph.