PORTLAND — Federal prosecutors have submitted a “substantive proposal” to the Portsmouth Naval Shipyard worker accused of setting fire to a nuclear submarine, according to a court document.

Casey James Fury, of Portsmouth, N.H., is charged with two counts of arson in the May 23 and June 16 fires at the shipyard. The May 23 fire caused an estimated $400 million worth of damage to the USS Miami, which was at the Kittery shipyard for a 20-month overhaul.

Federal Defender David Beneman wrote in the document that significant progress has been made in discussions about reaching a resolution to the case without an indictment.

“An additional period of time is needed to review the proposal,” he wrote in a motion about Fury’s speed trial rights.

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