submarine
n. countable A2 Elementary US //ˈsəbmɝˌin// UK //sˈʌbməɹˌiːn// sub·ma·rine
n. a ship that can travel underwater. You use it for research, military work, or exploring the deep ocean.
n. a naval vessel capable of independent operation underwater. It typically functions through the use of ballast tanks to control buoyancy and depth.
The submarine dives deep under the ocean waves.
Scientists used a small research submarine to explore the wreckage on the sea floor.
Modern nuclear submarines can remain submerged for months at a time, providing a stealthy platform for both scientific observation and strategic military deterrence.
From sub- + marine.