We descended into the turret and the hatch was closed. The Diesel engines had already been stopped and the electric motors were now turning the propellers.
“Why are those big electric pumps working down there?” I asked.
“Pumping water into the ballast-tanks.”
“But doesn’t the water run into the tanks anyhow, as soon as you open the valves?” I asked the lieutenant.
“Turn a tumbler upside down and force it down into a basin of water,” he replied, “and you trap some air in the top of the tumbler, which prevents the water from rising beyond a certain point. The same thing takes place in our tanks, and to fill them we have to force in the water with powerful pumps that compress the air in the tanks to a very small part of its original bulk. This compressed air acts as a powerful spring to drive the water out of the tanks again when we wish to rise. By blowing out the tanks, a submarine can come to the surface in twenty seconds or one sixth the time it takes to submerge.”
“When are we going under?” I asked him. The lieutenant looked at his watch and answered,
“We have been submerged for the last four minutes.”
I experienced a feeling of the most profound disappointment. Ever since I had been a very small boy I had been looking forward to the time when I should go down in a submarine boat, and now that time had passed without my realizing it.
“But why didn’t I feel the boat tilt when she dived?” I demanded.
“Because she went down a very gentle slope, between two and three degrees at the steepest. The only way you could have noticed it would have been to watch these gages.”