An 8 minute video, worth watching.
This submarine has no conning tower or sail. Very few submarines operate without a conning tower. The conning tower is needed to house the periscope with which the sub's crew can scan the horizon. If there is no conning tower the sub possibly has a "pop up" digital optical antennae which can scan the horizon and transmit the images via links to a computer (unmanned) or to an LCD screen located anywhere inside the sub (if manned). This means there need not be a captain standing exactly under the conning tower to see through the periscope. This frees up plenty of space inside the sub for other uses, like carrying more weapons.
If it is an unmanned submarine it will possibly be smaller in diameter and can probably dive deeper to evade detection. Without having to worry about endangering the lives of a human crew an unmanned sub such as this changes the equation completely. Imagine just a few of these submarines stalking an American aircraft carrier strike group. They can sink the entire strike group (NINE SHIPS IN THIS PICTURE PLUS ONE OR TWO SUBS UNDERWATER) at one go.
