As of 2009 yachts above 100 metres (328 feet) are still rare but increasingly more common. They typically have five decks above the water line and two below. The very largest yachts have begun to incorporate such features as helicopter hangars, indoor swimming pools and miniature submarines. The burgeoning number of "small" super yachts has led to the introduction of the hyperbolic terms Mega Yacht and Giga Yacht to demarcate the elite among luxury yachts.