Question

why submarines are made up of strong metals ​

Answer 1

Because submarines are made to travel under water and under water as depth increases the pressure also increases so , to prevent the submarines from that pressure they are made up of strong metals.

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Answer 2

As submarine need to dive very deep in water so it needs to be very heavy in weight and to prevent it from any corrosion or breakage

Above principle shows the increase and decrease in pressure and plus it needs to resist the high pressure inside the ocean as well so it's made up of strong metal and made heavy in weight