After refitting at Saipan, Greenling sailed north as part of the tightening U.S. submarine net around Japan’s home islands. Her mission was straightforward but perilous: interdict shipping along Japan’s coastal lanes and disrupt the remnants of enemy supply traffic fleeing the Philippine front.

The patrol began with quiet days of endurance and routine, constant radar sweeps, periscope observations, and the perpetual strain of aircraft alerts. Submariners of this late stage of the Pacific War lived in the shadows of their predecessors’ successes. Japan’s navy had learned, and anti-submarine air coverage was now relentless. Greenling frequently dived to avoid detection, her log marking dozens of aircraft contacts, many close enough to rattle the boat with their depth-charges.