| It is customary for a nation to ask diplomatic permission before entering territorial waters with a warship. OTOH maritime law is fairly clear: --- According to Article 19 (2) of UNCLOS, passage of a foreign ship shall be considered prejudicial to the peace, good order or security of the coastal state and thus in non-innocent passage if, in the territorial sea (less than 12 nautical miles from shore), it engages in any of the following activities: (a) any threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State, or in any other manner in violation of the principles of international law embodied in the Charter of the United Nations; (b) any exercise or practice with weapons of any kind; (c) any act aimed at collecting information to the prejudice of the defence or security of the coastal State; (d) any act of propaganda aimed at affecting the defence or security of the coastal State; (e) the launching, landing or taking on board of any aircraft; (f) the launching, landing or taking on board of any military device; (g) the loading or unloading of any commodity, currency or person contrary to the customs, fiscal, immigration or sanitary laws and regulations of the coastal State; (h) any act of wilful and serious pollution contrary to this Convention; (i) any fishing activities; (j) the carrying out of research or survey activities; (k) any act aimed at interfering with any systems of communication or any other facilities or installations of the coastal State; (l) any other activity not having a direct bearing on passage. --- Just sailing through is usually not a problem even with a warship. In this case of course, both parties were making a statement. The British that they don't recognize the annexation of Crimea, the Russians that they don't care what the British think about it. |
This could have an extremely broad interpretation. Any military ship sailing through territorial waters with some passive wireless sensors, sonar, and temperature/salinity gauges could fall under this. Civilian ships as well if that info is later forwarded to the military.