Tragedy at sea
By Charles Bloomer, LCDR, USN (Retired)
On February 9, the USS Greenville, a US nuclear powered submarine, collided with a Japanese fishing boat, the Ehime Maru, causing her to sink. Of the thirty-five aboard the fishing vessel, 26 were rescued, 9 are still missing and presumed dead. Greenville was performing an emergency main ballast tank blow, a routine, yet dangerous, evolution.
Let me say up front that I have no inside information on this accident. What I know is what I have read in the open press. As a retired submarine officer, perhaps I can shed some light on this incident and squelch some of the misconceptions. Much of what I have read is overblown, irrelevant, or erroneous. The facts will not be known fully until the Navy completes its investigation. Until then, some things can be surmised, given an understanding of submarine operations. Nothing I write here should be construed as an excuse for what happened.
Operations at or near the surface are the most dangerous routine operations a submarine conducts. One of the difficult things about operating a submarine at periscope depth is the limited visibility afforded by a periscope. In low power, field of view is limited to about 32 degrees. Higher magnifications afford an even narrower field of vision. In addition, a submarine at periscope depth provides a view point that is very close to the surface of the water, limiting the distance an observer can see to the horizon. With 4 feet of periscope exposed, the distance to the horizon is a little over 2 miles. Increasing the periscope exposure (height of eye) to 6 feet increases visibility to 2.7 miles, 9 feet increases visibility to 3.3 miles.
The same calculation for height of eye shows the visibility of another craft beyond the horizon. Assuming the Ehime Maru has a masthead height of 25 feet (hull and superstructure above the waterline), the uppermost part of the craft would be level with the horizon at 5.5 miles.
Assuming a reasonable periscope exposure of 6 feet and a 25 foot masthead height on the fishing boat, the top of the fishing craft would be just visible at 8 miles. This assumes clear visibility and a relatively calm sea. Reports during the rescue operations said that search for survivors was hampered by poor visibility and rough seas. The presence of haze and chop could hamper the ability to see a small, light-colored vessel.
Sonar is not 100 per cent capable of hearing everything in the water. Despite significant technological advances in sonar, the ability to hear is still driven by natural conditions that are sometimes hostile to the listening ship. The path that sound must travel through the water is highly dependent on the temperature of the water and the complex thermal layers that exist. A severe thermal layer near the surface can trap sound, preventing it from being heard below the layer.
Active sonar would likely not have been any more useful. Sound waves travel in the same path in both directions. If conditions prevented the sound from the fishing boat from reaching the submarine's passive sensors, those same conditions would have restricted the return path of the active sonar ping. Additionally, fishing boats generally have a very shallow draft. With little hull below the waterline, a small craft offers a very small target from which the active signal can reflect. Any echo from Ehime Maru would have been weak, and easily lost in the ambient noise that surrounds a submarine.
Much of the press reports are hyperventilating because there were civilians aboard. The presence of civilians on board is not unusual. The Navy engages in public relations, as do all the services. This allows the Navy to provide nonmilitary people a chance to see what ships do. Rides on submarines are frequently offered to journalists, civic groups, politicians, dependents and others. I have personally participated in submarine rides for high school students, dependents, even the Japanese Minister of Defense. The reports that civilians were sitting at the ship control stations, or that a civilian guest actually pulled the operators to initiate the emergency blow are not significant. Qualified crew members would be standing close by, ready to take control of their watchstations should anything unusual occur. Submarine crew members know how to control non-qualified personnel - they do it regularly as they train new crew members.
A submarine engaged in an emergency blow is very nearly uncontrollable once it starts its ascent. Blowing all the water from the ballast tanks make the submarine very positively buoyant. Within seconds, the ship becomes hundreds of tons lighter. This positive buoyancy generates a tremendous amount of momentum so that an 8000 ton submarine can actually clear the water as it surfaces. It is nearly impossible to prevent the ship from surfacing once the blow has started. Normal procedure calls for the rudder to be amidships and the fairwater planes to be on full rise. Stern planes are used to help control the ship's attitude.
What I have covered here are not excuses, merely observations. Submarine operations are hazardous, even in peacetime. Submarine captains know the dangers, as do the crews. Submariners are highly trained, and their training never stops. Crews drill continuously to develop and maintain the proficiency required to operate these increasingly complex ships.
With the prestige that comes with command comes absolute accountability. Every skipper knows that he is responsible for his ship and his crew, and that he will be held accountable should something untoward happen. Every ships captain knows that the two incidents that are career-stoppers are collision and grounding. No one should be surprised that Greenville's commander has been relieved of his command. Whether through negligence, or just plain bad luck, his career is over. The system is unforgiving because the sea is unforgiving.
This is an unfortunate tragedy, made worse by the loss of innocent lives aboard Ehime Maru. It seems almost inconceivable that, with the millions of square miles of ocean, these two ships would be at the same place at the same time. We cannot obliterate the pain of the families who lost loved ones, nor can we fathom the pain of the Greenville Commanding Officer and his crew. We can pray for them, and thank God it wasn't worse.
The Navy's investigation will be thorough and complete. The lessons learned -- expensive lessons -- will be used to try to prevent this from ever happening again.
Submarining is a dangerous business; the sea tolerates no mistakes.
Charles Bloomer is a retired US Navy submarine officer and senior writer for Enter Stage Right. He can be contacted at firstname.lastname@example.org. (c) 2001 Charles Bloomer
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