Ceto 4 deviated a long way from the original concept developed...

Ceto 4 deviated a long way from the original concept developed by CWE.

The main difference was that it was made up of interlocking plastic panels which made it buoyant. Because it was buoyant, it had to be dragged below the surface rather than submerging by filling with water as is the case with Ceto 3,5 and 6.

As mc stated, it lacked a fail/safe mechanism as well.

This image should give you an idea of what not to do in building a buoyant actuator.