Common loanword for a submarine vessel. Used in general, military, and technical contexts.
サブマリンが深海を探査している。
The submarine is exploring the deep sea.
その映画はサブマリンの乗組員の話だ。
That movie is about the crew of a submarine.
The submarine surfaced on the sea.
He rode in a submarine for the first time.
The researchers dove into the deep sea in a submarine.