For surface navigation, she showed above the water surface the bridge of 8.15 m long, 1.70 m wide and about 6 m high; part of the hull; and the upper part of the aft steering rudder. She was operated by delivering steering and engine orders from the bridge to the central operation center (conning tower) and the motor room, respectively, to alter course and change speed.
The Maritime Self-Defense Force, Submarine Flotilla 2 belongs to the Fleet Submarine Force of the Maritime Self-Defense Force, Self-Defense Fleet, and is composed of the headquarters of the said flotilla, submarine rescue vessels, and Submarine Divisions 2, 3 and 4 and the Yokosuka Submarine Base, and was engaged in the provision of training and instruction for submarine crew members in the same flotilla.
The "Nadashio" manned with the Commander of Submarine Flotilla 2, the Commanding Officer, designated person in the marine accident, and other 73 crew members started her return trip after an exercise of deployment of the Self-Defense Fleet NE of Izu O Shima on July 23, 1988.
At about 14:45 hours on the same day, the Commanding Officer went to the bridge about 2 miles south of the Uraga Suido Traffic Route and took command of the vessel and with the weapon officer and two other crew members posted as lookouts, he proceeded northward along the Uraga Suido Traffic Route at a speed of about 10.8 knots with the engine full ahead. When the vessel reached a point about 290°610 m from Uraga Suido Traffic Route No. 5 center light buoy at about 15:33 hours, he set her course on 270°
At about that time the Commanding Officer was in a situation where he could visually observe both "Eve I" about 27｡?o her port 1,050 m off, running northward under sail in waters west of the Uraga Suido Traffic Route and the "Fuji Maru No.1" about 28｡?o her starboard 1.4 miles, running southward in waters west of the Uraga Suido Traffic Route No. 5 light buoy at the north boundary of the same route. Although a lookout took notice of the presence of the "Eve I" and reported to him to that effect, he did not pay attention to the report and continued sailing westward unaware of the two boats.
At around 15:34 hours when the "Nadashio" cleared out of the western boundary line of the Uraga Suido Traffic Route, the Commanding Officer first sighted the "Fuji Maru No.1" about 29｡?n her starboard bow 1 mile off, and at about 15:35.5 hours, the "Eve I" about 300 m off her port bow. Assessing that his submarine could clear ahead of the "Fuji Maru No.1" safely, he failed to keep track of her movement properly thereafter and was not aware that the pleasure fishing craft was drawing near, involving risk of collision. Since his vessel developed a close quarters situation against the sailing boat, he stopped the engine and sounded a long blast about 15:36 hours. The "Eve I" made a port swing and the danger of collision with her was eliminated; and the "Nadashio" proceeded without taking action to avoid collision with the "Fuji Maru No.1".
Since the Commanding Officer was still under the wrong impression that he could pass ahead of the "Fuji Maru No.1" without sufficiently ascertaining her movement, he ordered "Full ahead engine" slightly before 15:37 hours and the Nadashio was accelerating her speed, when, slightly after 15:37 hours, he suddenly realized the imminent danger of collision with the pleasure fishing craft as she neared to a distance of about 400 m.
