One early stabilization technology is the anti-rolling gyro, or gyroscopic stabilization. The World War I transport USS "Henderson", completed in 1917, was the first large ship with gyro stabilizers. It had two 25-ton, 9-foot diameter flywheels mounted near the center of the ship, spun at 1100 RPM by 75 HP AC motors. The gyroscopes' cases were mounted on vertical bearings. When a small sensor gyroscope on the bridge sensed a roll, a servomotor would rotate the gyros about a vertical axis in a direction so their precession would counteract the roll. In tests this system was able to reduce roll to 3 degrees in the roughest seas. One of the most famous ships to first use an anti-rolling gyro was the Italian passenger liner , which first sailed in November 1932. It had three flywheels which were 13 feet in diameter and weighed 108 tons. Gyroscope stabilization was replaced by fin stabilization due to its lower weight and bulk, but it has seen renewed interest since the 1990s (Seakeeper, etc.).