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In a Twitter post, a respected Turkish ship spotter showed evidence that a Russian Kilo-class submarine allegedly passed through the Bosphorus, in violation of the Montreux Convention. At press time, we were unable to confirm the report independently, however, if true, the news would be very significant.
(Apparently it sailed on the surface.)
Upvote:9
Information provided by user999999.
According to Halpern, The Mediterranean Fleet, 1919–1929, p. 96, the British submarine HMS E46 made a passage in 1919 at periscope depth (or slightly above), and concluded submerged transit undetected would not be possible/practical.
Addition, context: in 1919 Istanbul was occupied by the WWI victors, so this does not really count as a "hostile" passage.