I went and found the letter. From reading it, the situation smells like someone made a political decision to hide the carrier's disability. That decision meant denying the personnel aboard were condemned to the disease running it's course and that ultimately would likely expose the carrier's complete disabling as well as costing the country the loss of a lot of very expensive people to replace. I suspect that Crozier was already looking at a direct rebuke from at least one superior without the balls to stand up and do the right thing. Navy line officer captains do not get there by making seat of the pants dumb decisions. They understand what politics is all about, and most particularly Carrier captains.
With all of the cryptographic equipment at his disposal making a situation report and readiness status over secure means was a no brainer. He made a statement that he felt was necessary for the good of the country, and did so knowing that it was the end of his career. There will be political fallout from this and it is going to take out some of the people above him who forced his hand. Likely some civilian and some military. Crozier is done, but I am pretty sure his last action was honorable.
