A sperm. Whale is capable of diving to. A depth of 1. 2 miles
Before a deep dive, a sperm whale takes a breath (obviously). This makes it more buoyant, which is not good for diving. However, with a flick of its tail, it dives deep enough for the pressure to squash its lungs enough to make it negatively buoyant. It therefore sinks, taking little effort to dive to such depths.