ultrasonics-operated mine
1tunnels and underground excavations — ▪ engineering Introduction Great tunnels of the world Great tunnels of the worldhorizontal underground passageway produced by excavation or occasionally by nature s action in dissolving a soluble rock, such as limestone. A vertical opening …
2Battle of the Atlantic (1939–1945) — Infobox Military Conflict conflict = Battle of the Atlantic partof = World War II caption = Officers on the bridge of an escorting British destroyer keep a sharp look out for enemy submarines, October 1941 date = September 3 1939 May 7 1945 place …
