Sentencing Twitter abuse pair Isabella Sorley and John Nimmo, Judge Howard Riddle said it was "hard to imagine more extreme threats."
The pair admitted sending a series of abusive message to feminist campaigner Caroline Criado-Perez.
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The country's top defence officer said the force may ignore any order to launch a nuclear attack which is deemed to be illegal.
Navy officials say they have received seven short satellite calls which are though to have come from the submarine.
The President is to meet with with the army commander who put him under arrest as he resists calls for him to stand down.