The sperm whale was hunted voraciously up until 1988 for the waxy spermaceti oil in its cranium. It was found to be an exceedingly fine lubricant for machinery because it has interesting temperature-dependant density and viscosity properties. It is generally believed that the whale regulates these properties to mediate its buoyancy allowing it to easily dive when the oil is denser than water and helping them surface when it is less dense.
The energy economy of this exchange facilitates dives as deep a 3km (almost 10,000 feet) making the sperm whale the deepest diving vertebrate known. (Pressures at 3km are over 4400psi or 300 atmospheres.)
The spermaceti organ is also has very complex acoustical features, allowing the focused transmission and reception of their characteristic bio-sonar. The sperm whale “clicks” when heard in aggregation sound like a busy team of carpenters hammering away on a job – giving them the colloquial name of “carpenter fish.”
The sperm whale, like the gray whale (and unlike any of the other whales) will attack their aggressors, which made the fishery exceedingly dangerous for whalers (although even more dangerous for the whales). (From OCR)
Sperm whale buzz
Sperm whale calls