Around the World Submerged: The Voyage of the Triton

As Triton ballooned upward, I watched silently for signs of the required action. It is for situations like this that men are qualified in submarines. With approval, I saw Rauch keeping his eyes on Harris, his hand already resting lightly on the controls for the main vents. Thamm was watching, too. Triton rose at an ever-increasing pace and finally Dick gave the order: “Open main vents.”

I could hear the vent mechanism operating and all of us heard the rush of the entrapped air as it escaped from the tank. But Dick was still watching the depth gauges, “Shut main vents,” he ordered. His objective was to catch some of the air still inside the tanks in order to retain some of the resulting buoyancy. In the meantime, with approval, I noted that he had not ordered Rauch to stop the trim pump, that we were still pumping water from the midships auxiliary tanks to sea.

Triton’s rise toward the surface ceased rather abruptly. By this time, we had no forward motion through the water at all. With the ship badly out of trim, she was controllable in depth only by the constant buoyancy of her great hull, plus the variable buoyancy of the expanding and contracting volume of air in the ballast tanks. Undersea ballooning was an apt simile.

But Dick had let out too much air, for Triton was now heavy and began to sink once more; as she sank, the air bubble remaining in the ballast tanks would be further and further compressed, with the result that the ship’s buoyancy would continue to reduce and she would now progressively descend faster and faster—though slower than the first time. Dick was ready for this, however, and after we had sunk some little distance, he again ordered that tanks be blown, but for a considerably shorter time than before. Again, Triton halted her descent and began to rise; and, as she neared the surface, Dick opened the ballast tank vents and allowed most of the air to escape.

In the meantime, we had continued pumping water out of the ship. Gradually, our wild gyrations lessened as we got her correctly trimmed. With ballast tanks again full of water, no air trapped in them, Triton finally hovered, motionless, balanced precariously with her internal weight exactly equal to that of the water displaced.

It might be well to explain at this point a fact that submariners know well, but which may not be so well known to others: it is impossible for a submerged body to be so delicately trimmed or balanced that it will remain indefinitely static, neither rising nor falling. Despite fanciful tales written by people who do not know their physics, things cannot just sink part way. A submerged submarine has no reserve buoyancy; that is to say, she gains no additional buoyancy by sinking a little deeper in the water (a surface ship, passing from more-dense to less-dense water, increases imperceptibly in draft). If an eight-thousand-ton submarine is one pound heavier than the water she displaces, she will slowly sink. The deeper she goes, the greater the pressure; even the strongest hull will be slightly compressed, thus reducing the volume of displaced water and increasing the disparity between her weight and that of the water displaced. She will go all the way down until she reaches the bottom. Conversely, a submerged submarine one ounce light will ultimately broach the surface. The only exception to this rule occurs when there is a layer, or stratum, of heavier water underlying a lighter layer. In this case, the submarine can “balance” on the boundary between the two, as long as the dissimilarity continues to exist. This is known as “riding a layer.”

It is true that a submarine almost in perfect trim—as near to perfect trim as it can possibly get—might very very slowly sink in water of a certain density until it reaches a layer of water considerably cooler or more saline than the one for which trimmed, and there she will stay for a while. Ships have been known to ride thus, suspended between two layers of water of dissimilar densities, for many hours. There have even been stories about balancing a submarine so skillfully that the slight increase in displacement gained by raising a periscope would cause her slowly to drift toward the surface, and sink slowly when the periscope is withdrawn inside its bearings, but, practically speaking, such situations are rare and highly temporary.