Submariners.
U-boat
Submarines typically use air tanks. Oxygen is very dangerous and very flammable. It's use is very limited on submarines for that reason.
Submariners.
They are called submarines
submarines and bats both use sonar. Calvin was here
oceanographers use submarines to take pictures of sea life and things that have been found or things that they are looking for.
The marines do not use submarines. Only the Navy does.
Most submarines have propellers that spin, pushing them forward. A few smaller research submarines use a water jet for propulsion.
The Germans were the first to use Submarines in World War 1. Now i believe that the marines now do at times.
Sinking ships; exploring the depths.
Yes, they did.