Armed Forces on 19 APR in LV EEZ 8 nmi from territ. waters spotted RU Navy's Kilo-class submarine.— NBS (@Latvijas_armija) April 19, 2015
The Kilo-class type of submarine is NATO's term for the Russian-made anti-shipping and anti-submarine vessel designed for use in relatively shallow waters. Besides torpedo and mine-setting funcitons, these diesel-electric powered subs can also be equipped with anti-aircraft missiles.
Just two days prior, on Friday the NATO Baltic Air Police (BAP) scrambled to intercept a Russian anti-sub and patrol plane, the Ilyushin IL-38 in international airspace near Latvia's Baltic Sea borders.