"Except that it appears to have been a diesel - electric boat (Golf), which would fairly definitively rule out a reactor failure."
Yeah, that could present some obstacles to that possibility. 8) No mention of Golf-class in the article, though 'nuclear sub' was rampant. Nuclear MISSILE sub would have been more accurate.
Others on this thread have floated the idea of a US/Soviet sub crash. One would assume that one sub tracking/being tracked by another would maintain radio silence. It fits the facts pretty well, too. That would be another decent scenario, one I'd still think more likely than the "mad Russian cap'n" scenario,
what is the possibility of a torpedo malfunction?
a malfunction of the warheard, or a fuel handling
accident?
The main problem you run into with the collision theory is the same one you run into with the Kursk. There was such a disparity in damage between the Russian boats that were lost and the American boats which needed only minor repairs at the same time. (I think the Swordfish had only a damaged periscope, and continued its patrol after repairs).
I personally favor the 'accident while charging the batteries' scenario.