ABOT - The Automatic Builder of Towers

Humans have always been quite useless under water. But what happens when they start needing under-water towers or bridges built across the ocean? 

The Abot dives deep into the ocean and builds an under-water tower as tall as one might need! It can also be fitted with the new ecological permion propulsion units (PPU) to work on land!

Video demo:

(The hand stands in for real-life buoyancy)