The Second Investigation Department or AOTD (Lithuanian: Antrasis operatyvinių tarnybų departamentas) is a Lithuanian intelligence agency under the Ministry of National Defence.

[1] The origins of the institution are in the Intelligence Unit established within the Lithuanian Armed Forces on 27 October 1918.

In 1923, many intelligence activities were transferred to the Ministry of the Interior forming what later became the State Security Department of Lithuania.

Military and defense related intelligence stayed within the General Staff and after 1929 the service was reorganized and named the Second Unit.

[2] Its early task was to gather intelligence on Soviet military units operating in the region.