An unmanned semi-submersible vehicle developed at Washington State University may prove that the best way to travel in water undetected and efficiently is not on top, or below, but in-between.

The roughly 1.5-foot-long semi-sub prototype, built with off-the-shelf and 3D-printed parts, showed its seaworthiness in water tests, moving quickly with low drag and a low profile. The researchers detailed the test results in a study published in the journal Unmanned Systems.