From experiences with Sea Colonies in the 22nd century engineers developed a new appreciation for the construction of ultradeep craft. Designed to collect magnesium nodules from the sea floor and later to dig undersea mines, these vehicles survived seven miles beneath the sea at over a thousand atmospheres of pressure. Later, military engineers created modified craft for carrying troops along the ocean floor that were virtually invisible to sonar or radar. The result: ocean chaos, piracy, and war.