Only if they sink beyond their stress limit (crush depth). Subs are built to withstand the pressures very deep and will not "implode" unless they sink in very deep water. Don't forget; It is very rare for a submarine to sink with its pressure hull intact. Why would it sink when it is not taking on water? When it is taking on water and sinking, the water will enter the submarine at enormous pressures so the submarine will be flooded before it implodes. If, during the sinking, a compartment was sealed off from the compartment that is flooding it could implode but normally something else will give way (a hatch or a pipe) and so that compartment will also be flooded.
All submarines can sink. Some can return to the surface.
Ships try to avoid sinking, submarines sink on purpose...
They caused anxiety and sink ships.
sink allied supply ships to England
They were at war with each other.
To sink enemy vessels, ships or submarines.
A number of nuclear submarines sank, and the circumstances vary from accident to accident. Wikipedia has a list, and by going there and entering "List of sunken nuclear submarines" you can review that list.
No, India will get annihalated by the Chinese submarines. Unless you pay me big bucks to come a sink all of there submarines.
They were used mainly to sink enemy transport ships.
To stop supplies from reaching England
Submarines sink vessels by using stealth (hiding).
There are now 'Attack' submarines who's main purpose is to sink enemy submarines and ships and also Missile submarines whose main purpose is to launch ballistic missiles at the enemy.