USS Greeneville/Ehime Maru Collision Update

The following is updated factual information documented by NTSB investigators in Washington, D.C. since the departure of the Board's investigative team from Hawaii on February 24.

The USS Greeneville was equipped with a sonar data logger that recorded sonar data and "own ship" data once per second. Data for the accident were transferred to a data tape (normally used for archiving data). This data tape is en route to NTSB headquarters for analysis. However, the Navy has provided the NTSB with a preliminary data file containing parameters extracted from this tape. Heading and keel depth from this data file are plotted for a 10 minute period that includes the collision in figure 1. The NTSB has not applied any instrument corrections to these data.

• These data show the Greeneville ascending to an initial periscope depth (uncorrected instrument readings ranged from 63 to 67 ft keel depth) at about 23:38:30 UTC (1:38:30 Hawaii time).
• The Greeneville then ascends about 3 ft higher in the water (using uncorrected instrument readings) about 1 minute later for a total time at periscope depth of about 1 ½ minutes.
• This is consistent with witness statements.
• At 23:40 the Greeneville commences its descent from a heading of 120 deg. At about 23:41 the Greeneville begins a heading change to port (left). She reaches a maximum depth of about 405 ft at 23:42 on a heading of 028 deg.
• At 23:42:30 the Greeneville begins its rapid ascent to the surface and collides with the Ehime Maru at about 23:43:20. At impact, the Ehime Maru was on a heading of 166 deg while the Greeneville was on a heading of approximately 018 deg.

Figure 1: Preliminary Greeneville Depth and Heading

Although the submarine's position was not recorded, it is possible to derive the Greeneville's track from recorded heading, speed and pitch data. Figure 2 shows this derived track with the radar track of the Ehime Maru.

• The plot shows the track of the Greeneville first heading South (light blue) and then heading North (dark blue) toward the accident site.
• Prior to rising to periscope depth (shown in figure 1), the Greeneville executes a series of turns.
• The plot shows only the last 18 minute segment of the radar track of the Ehime Maru prior to the collision. Radar shows the Ehime Maru was traveling 11 knots on a heading of 166 deg. This is consistent with the statement of the ship's master.
• The plot then shows the Greeneville turn towards the Ehime Maru shown in figure 1, the collision, and finally the Greeneville's return to the accident site.

 
Figure 2: Preliminary Greeneville and Ehime Maru Track

Figure 3 shows the radar track of the Ehime Maru and the last 15 minutes of the derived Greenville track before the collision and the Greeneville's return to the accident site on the surface in 3 dimensions. The surface dimension is 2 ½ by 2 ½ nautical miles.

Figure 3: 3D view