To smash through solid Arctic ice, a multi-billion-dollar nuclear submarine doesn't ram it at high speed. It actually comes to a dead stop.
Submarines cannot punch through just any section of the polar ice cap. The ice at the North Pole can be tens of feet thick, acting like an impenetrable concrete ceiling. Crews must use upward-looking, high-frequency sonar to map the underside of the ice canopy. They search for "polynyas" or ice leads—stretches of open water or areas where the ice is relatively thin, ideally three feet thick or less.
Once a suitable spot is located, the submarine begins a slow, vertical ascent. Preparation is critical to avoid snapping off vital external components. Antennas and periscopes are fully retracted into the sail (the tower on top of the submarine). The sail itself is constructed with hardened steel specifically reinforced to withstand crushing forces. On classes of submarines designed for frequent Arctic operations, the horizontal diving planes located on the sail can be rotated to a completely vertical position. This aligns them with the sail so they are not torn off by the ice. Other submarines bypass this issue entirely by placing the diving planes on the bow instead of the sail.
The actual breakthrough is achieved by buoyancy rather than speed. The crew slowly pumps water out of the submarine's ballast tanks. As the vessel becomes lighter, its massive hull presses up against the bottom of the ice. A modern nuclear submarine displaces thousands of tons. Transferring that immense upward buoyant force into the hardened tip of the sail concentrates the pressure on a small area. The ice slowly bows, fractures, and finally shatters under the static pressure, allowing the sail to push through to the frigid polar air.
This deliberate maneuver requires immense patience and can take hours. Rushing the process could severely damage the anechoic tiling on the hull or crush the sail, leaving the submarine damaged and trapped beneath the Arctic ice cap.