The sun had barely set on June 30, 1942, as USS Sturgeon continued her patrol northwest of Cape Bojeador, slipping beneath the waves at dawn and surfacing at dusk as she had done for days. The ocean was quiet, routine. But just after 10 PM, the monotony broke. The watch spotted a darkened ship to the south, cutting through the sea under the cover of night.

At first, the angle of the sighting made it seem like the vessel was heading north, but careful observation quickly corrected that. She was moving west at high speed, clearly having just exited Babuyan Channel and making for Hainan. This was no dawdling freighter. She was moving fast, at least 17 knots, and zigzagging to avoid detection. A valuable target.