A portion of the Sakaguchi Detachment called the Surprise Attack Unit proceeded up the river in camouflaged landing craft, evaded detection, and landed just south of the reservoir at 04:30 on the 25th. It proceeded to the village of Banoeabaroe, arriving there at 14:40, thus cutting off the Dutch line of retreat. While the unit was advancing along the road to Balikpapan City, it ran into a Dutch military column, commanded by Lieutenant Colonel C. van den Hoogenband, attempting to escape from Balikpapan. After defeating this Dutch column, the Surprise Attack Unit proceeded to Balikpapan City.