Indicating where suspected Russian mini-submarines were detected near Helsinki Harbour (late April 2015) and near Stockholm (October 2014 and January 2015).
---
Helsinki Harbour. Suspected Russian (probably) mini-submarine detected late 2014. There would probably be sea-floor anti-submarine sensors arrays outside Helsinki Harbour (like Sweden's Malsten array).
---
HNGN, April 28, 2015 reported: "Our sensors detected something, an uncertain underwater object, at lunchtime on Monday April 27, 2015] and then again overnight," Captain Olavi Jantunen told Helsingin Sanomat newspaper, reported the Guardian."Three [grenade] charges were dropped, but they were warning charges, with a light burst, meant to warn rather than do any harm to the object."
Jantunen said it's impossible to determine what the object was until a complete analysis has been performed on the sensor data, which could take as long as three weeks [takes about 3 minutes], according to the Guardian.
The [Finnish] defense ministry issued the following statement: "As part of the tasks to protect territorial integrity, the maritime surveillance system alerted the Finnish Navy of a possible underwater target around midday on 27 April 2015. The possible target was located within territorial waters, close to the limit of territorial waters off Helsinki. A search was then conducted by surface vessels."...
BACKGROUND AND COMMENT
The (probably) Russian mini-submarine or large diameter unmanned undersea vehicle (LDUUV) may be there to "trip" or test Finnish sensors or to make Finland politically nervous. This is like the Russian aircraft incursions - part of Putin's confrontational style. The mini-submarine may be a development of Russia's Losos-Pirana.
The Finnish Navy would have determined very quickly - via tell-tale sensor "signatures" - what type of undersea craft has trespassed Finland's territorial waters. For diplomatic-political reasons Finland would not accuse the trespasser, particularly if it is powerful and combative Russia. Though part of the European Union Finland maintains a careful neutral policy.
The "sensors" used to alert the Finnish Navy may be hydrophones, magnetic anomally and other wireless or fixed sea-floor arrays deployed inside Finland territorial waters. Nokia Data Systems equipped the Finnish military with an integrated coastal surveillance system - according to late 1990s reports. This system would now be very high-tech with many of the sensor uprgrades and increased computer processing power available today. Even quite a small mini-submarine or LDUUV can be detected. Sweden's has its own Malsten Station array which no doubt is much improved since the 1980s.
The grenades used may be Saab ASW-601s [right-click mouse to translate to English] fitted to multiple grenade launchers on such Finnish vessels as the Hamina class missile boats. These grenades may have been aimed away from the suspected submarine/LDUUV or have adjustable burst features.
See Submarine Matters reports of October 25, 2015 and January 15, 2015 on Sweden's late 2014-early 2015 experience of suspected Russian mini-submarines or LDUUVs.
Pete