But a Navy official familiar with the situation but not authorized to speak publicly about it said that the captain had repeatedly asked his superiors for speedy action to evacuate the ship. His letter, the official said, came because the Navy was still minimizing the risk.

Mr. Modly insisted that his firing the captain for writing a letter asking for more help does not mean that subordinate officers are not allowed to raise criticisms and ask for assistance. “To our commanding officers,” Mr. Modly told reporters on Thursday, “it would be a mistake to view this decision as somehow not supportive of your duty to report problems, request help, protect your crews, challenge assumptions as you see fit.”

But the removal of Captain Crozier will likely have a chilling effect on the willingness of commanders to bring bad news to their superiors.