the water pressure acts as a crushing force. if you was to squeeze a loo roll it will squash. if it was solid you woluld not be able to crush it as the mass would just redistribute. also if there was an opposing force pushing against your crushing motion then the loo roll would remain unchanged wether it was solid or not. this is why the submersible can sucumb to the high pressure while simple clocks wont. the submersible has air inside which has to be very high pressure to counteract the pressure of the water. if the submersible just dived without pressure regulators then the air inside will not be sufficient and the structure would collapse. the clock has no water tight compartments and thus the force of the water pressure on the outside of the clock is counterbalanced by the force of the water pressure inside the clock which is equal to that of the outside.
on a seperate note, if you were to dive to about 10 meters depth without the use of a submersible, diving bell or anything, then you would find that instead of floating as most people do, you would sink. this is where the pressure overpowers the bouyancy of the air in your lungs.
