Because they need to be able to withstand the pressure of the seawater outside. The deeper a submarine goes - the higher the pressure gets.
To withstand the external pressure.
As a submarine submerges, it is subjected to a high volume of water pressure, which increases the further in depth the submarine goes. They have to be built to be able to withstand this pressure.
To withstand high water pressure when they are submerged at sea.
4mm sheet metal falls 24 gauge and 25 gauge. 24 gauge sheet metal is 3.175mm (0.125") thick, and 25 gauge sheet metal is 6.35 (0.25") mm thick.
There is a need to put a countersink on sheet metal before you use a cutting tap. Even if the sheet metal is 089 thick, it is recommended for safety any amount of thickness.
0.0747 inch. or 1.89 mm
US Destroyers were built of less than an inch thick of sheet metal. US Battleships, Carriers, and Cruisers had belts of "armor" around them, and were often over an inch thick in sheet metal (skin). Therefore, US Sailors called destroyers, "TIN-CANS"..."Cans" being short for Tin Cans.
we can weight one sheet and calculate the unit weight we can weight one sheet and calculate the unit weight
The price will depend upon the length and thickness you get. One-fourth inch thick sheet metal that is 1 x 2 feet is close to $20.
tinsnips or power tool called a nibbler or welding/cutting equipment if rather thick metal
Her is a link to a chart of all guages... http:/www.unc.edu/~rowlett/units/scales/sheetmetal.html #26 wire is .0159 thousandth of an inch or .405 mm in diameter. This is for AWG wire sizes which is different from the steel industry which use a different numbering system for their wire thickness gauges.
A thin sheet of metal will produce a higher pitch when struck compared to a thick sheet of metal. This is because thinner materials vibrate more easily and at a higher frequency, resulting in a higher pitched sound.