AT&T Submarine Systems Inc., Morristown, NJ, has successfully transmitted 10 gigabits per second on segment B, a 2000-kilometer link of the Columbus-II submarine cable system. This system spans 13,000 kilometers and will provide service to Mexico, the United States, Italy, Portugal and Spain when it is activated this month. Segment B extends from West Palm Beach, FL, to Magens Bay in St. Thomas, U.S. Virgin Islands. It employs optical amplifier technology developed at AT&T Bell Laboratories. The Columbus-II results are significant because the tests were performed on a commercially installed system. Special tests included various transmission formats such as wavelength-division multiplexing. The Columbus-II cable system proved that it is possible to upgrade an installed fiber-optic communications system without making any adjustments to the portion of the cable system on the sea floor. The experiment quadrupled the transmission capacity of the system, which normally operates at 2.5 billion bits per second.