A merchant sailor was found guilty of manslaughter after his ship crashed into another vessel off Hastings, killing its captain.
Judge Richard Brown jailed Brian Norcutt D'Esterre-Roberts for 12 months.
D'Esterre-Roberts was convicted of unlawfully killing Wolfram Gross in the crash of October 2001.
He was watch officer when his ship, the tanker Dutch Aquamarine, smashed into the Ash, which was carrying a cargo of steel.
The Ash sank minutes after the collision and its crew had to abandon ship. Its captain, Mr Gross, was winched from the sea by a helicopter and later died.
D'Esterre-Roberts, from County Cork, Ireland, failed to notice that his ship was following a collision course with the Ash for more than an hour before the crash, Lewes Crown Court heard.
The judge told D'Esterre-Roberts: "By their verdict the jury have found that your breach of duty was of such a degree that it showed a total disregard for the lives of others and therefore amounts to a very serious crime.
"On the other hand, at least you had during the course of your interviews the courage to admit your degree of negligence.
"You are a man of excellent character with a good work record. You are unlikely to offend again and it is right to say that this was a crime of omission and will remain on your conscience for the rest of you life."
John Astbury, director of operations at the Maritime Coastguard Agency, said: "This tragic incident clearly demonstrates how vitally important it is for any person who is in charge of the navigation of a vessel to maintain a proper and effective lookout.
"D'Esterre-Roberts' standard of watch-keeping fell so far below the level required that this collision was inevitable."
D'Esterre-Roberts denied manslaughter but admitted breaching or neglecting his duty.
The jury returned a majority verdict.
Second officer D'Esterre-Roberts told the court how, in the minutes before the crash, he "lost concentration" while talking to Dutch cadet Nils Sandeford.
By the time he saw the Ash off the bow of his tanker, which was carrying acetic acid, it was too late to take action. The ship sliced into the Ash, holing her below the water line.
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