What is keel of submarine?

The keel of a submarine (or any ship for that matter) is the backbone of the ship, and its primary structural element. Keels are always laid first during shipbuilding, and structural supports are added over time to it. Laying a keel is typically done with a ceremony.

A keel is similar to a human spine, though it's on the bottom of the ship. Like a spine, it is the key support structure of the vessel; if a keel is broken, the ship usually will lose structural integrity altogether and sink. This is often what happens when ships run aground.

Breaking a ship's keel is also the primary method of how modern torpedoes work. Rather than just impact them, they swim under the ship and explode, creating an air pocket beneath the keel. The bow and stern of the ship cannot support the full weight of the ship in the middle, and the keel breaks, snapping the ship in half.