A $\backslash (1/5\backslash )-$scale model of a torpedo is tested in a wind tunnel to determine the drag force. The prototype operates in water, has $533$ mm diameter, and is $6\mathrm{.}7$ m long, The desired operating speed of the prototype is $\backslash (28\backslash$mathrm$\{$~m$\}/\backslash$mathrm$\{$s$\}\backslash ).$ To avoid compressibility effects in the wind tunnel, the maximum speed is limited to $\backslash (110\backslash$mathrm$\{$~m$\}/\backslash$mathrm$\{$s$\}\backslash ).$ However, the pressure in the wind tunnel can be varied while holding the temperature constant at $\backslash (20^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash ).$ At what minimum pressure should the wind tunnel be operated to achieve a dynamically similar test? At dynamically similar test conditions, the drag force on the model is measured as $618$ N $.$ Evaluate the drag force expected on the full$-$scale torpedo.