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1. Most Submarines are created solely for military purposes

Submarines according to the text, are created primarily for warfare with their main weapons being torpedoes that are like mini self-propelled submarines carrying an explosive charge.

2. Submarines either rise or submerge by displacing water.

Submarines use the Archimedes principle which works by displacing water that weighs more than the boat to rise.

3. Some submarines are used for Oceanic Exploration

Some or at least 1 at that moment being the Argonaut was built for oceanic exploration and is equipped with diving appliances and equipment to enable it save wreckage.

4. All submarines must be sure not to descend too far underwater.

Every submarine has a limit in terms of the depth it can submerge to and it should not go beyond this point. Water bodies have their pressure in them as sink deeper and if the submarines go beyond the point where the submarine can no longer withstand the pressure it will be battered.