How were they able to design such a complex ship?

Submarines evolved. They weren’t conjured up out of someone’s imagination as fully formed vessels in the 1930s and 40s. These WW2 submarines were the result of a rather lengthy process going back hundreds of years. Here is a quick summary, up to the beginning of WW2. 

The idea of a submersible, naval warship appears to go back at least to the reign of Alexander the Great. That was 300 years BCE (before the common era). Leonardo De Vinci also designed a submarine, although it did not appear to be workable.

The first attack in American submarine history was on a British ship during our Revolutionary War. It was attempted by David Bushnell’s submarine Turtle.  Like most of the designs at this time, Turtle was a small, one-man submersible powered by the man inside it. The weapon was called a torpedo but it was what we think of as a mine. It was to be attached to the target and detonated after the submersible pulled away to a safe distance. Because the speed and endurance were so limited, the attempted attack against a British ship failed.

The USS Alligator was the first known U. S. Navy submersible, purchased during the Civil War. (The Turtle, above, was apparently operated by the Continental Army.) It was also small and powered by the 12 men inside, first with oars, then with a hand-cranked propeller. Alligator did not contribute to the Civil War effort and sank off Cape Hatteras with no loss of life in 1863. (Wikipedia)

The first successful attack by a submarine was the sinking of the USS Housatonic. The Confederate submarine CSS Hunley successfully approached the Housatonic and detonated the spar charge. The Housatonic sank. Unfortunately, the Hunley was not able to get far enough away and the crew was all killed when the submarine also sank. This was the third crew of the Hunley to die when the vessel sank.

A breakthrough occurred in the late 1800s. Robert Whitehead had developed his motor torpedo, a self-propelled device that was a natural fit with the submarines being built. Shortly after that, at about the turn of the century, John Holland and Simon Lake were able to create workable submarines here in the US. Their boats had gasoline engines and were no longer dependent on human power. They were larger and Holland’s boats carried torpedoes.

It took years but Holland was finally able to get the Navy to approve his designs and buy his submarines. These would be the first mechanically-powered attack submarines. When he ran short of capital because of all the delays, Isaac Rice came to his rescue. Rice had been looking for more applications for his Exide battery business. Submarines were a logical application for batteries since that was their source of power when submerged. Rice bought out Holland’s patents and the rest of his financial interests. Holland was eventually squeezed out of the company altogether. This was the beginning of the Electric Boat Company which still builds U. S. submarines today. It was also the last of Holland’s designs.

Some nations bought Holland’s boats. Others bought the designs and developed their own boats. Britain and Germany built their own submarines based on what they learned from the Holland designs and Lake’s work. Many navies wanted to have their own input into the designs of their boats. Holland and Lake had done their own designs and offered the boats for sale.

By the time of World War I, there had been many improvements. Boats had periscopes and both bow and stern planes for depth control. They were larger. They were still somewhat primitive but more habitable. Germany, in particular, had created very effective boats. This became apparent in September of 1914, only about six weeks into WW1, when Otto Weddigen in command of the U-9 attacked three obsolete British cruisers in the space of about an hour. All three sank rather quickly with the loss of almost 1,500 men.

Germany then proceeded to show how effective a weapon of war a submarine could be. They almost severed the supply lines to Britain and France. British ships could find German submarines with ASDIC, which we call sonar. However, they were still developing weapons to attack subs in the depths. Escorts could only hope to ram submarines or force them to the surface and attack with guns. Sometimes, it was good enough to just keep the U-boats down and unable to attack while the convoy escaped.

Eventually, the Allies managed to defeat the Central Powers on land to end the war. As the spoils of war, the Allies received examples of the German U-boats. After the war, when we compared our new submarines to the German U-boats, we realized how limited our boats were. One analysis found that in every category the German submarines were superior. In many aspects they were far superior. We had no choice but to begin the work of improving our designs.

The two most basic issues were first to determine what types of submarines we should have and then finding an appropriate and effective means of propulsion for them. Some of the other lesser challenges we had to address were the quality of periscopes, communications, detection gear (sonar) and habitability over long distances

Perhaps the most important outcome of the analysis in 1926 was the creation of the Submarine Officers Conference. This was a group of experienced submarine officers that included senior commanders, naval engineers and officers who had commanded boats. For the first time, American submarine officers would have input into the needs of the submarine force and the designs of the submarines themselves.

By 1934, they had settled on a design of approximately 1,500 tons surface displacement. This would provide the range needed to carry the fight across the Pacific and Atlantic if needed. The boats needed to be large enough to carry the fuel for a long journey and to carry enough torpedoes to make the trip worthwhile. This would be the eventual size of the Gato/Balao/Tench class boats of WW2, such as the Pampanito.

The propulsion issue wasn’t easily solved. The surface navy at the time was primarily steam-driven and had difficulty imagining anything else. However, steam isn’t practical in a submarine dependent on fossil fuels. Restarting a steam plant after being submerged takes way too long. Keeping a steam plant running while submerged makes the submarine too hot for the crew.

NOTE: Our modern submarines do use steam for propulsion. However, since they are not using fossil fuels to produce the steam, they don’t need oxygen for combustion. The turbines are always using the steam, and the boat is most often at a reasonable temperature.

Gasoline was also impractical as a fuel source. It is too volatile; it tends to catch fire too easily and the fumes in a closed space are toxic and can be explosive.

The answer came from improvements in diesel engines. Then it was a question of the cost of designing and producing these specialized engines. Fortunately, railroads were also looking for diesel engines that would fit in their locomotives and produce a similar amount of power. The railroad engines were similar enough to those for our submarines so that they could spread development and manufacturing costs.

The Submarine Officers Conference opted to design the power transfer, from the engines to the propeller shafts, as mostly electrical. On our WW2 boats, the engines are not connected physically to the propellers. They were essentially electric submarines with four large engine/generator combinations to provide the electrical power. The arrangement and the flow of power is:

           [Engine] [Generator] ==> [Cubicle] ==> [Main Motors] [Reduction Gear] ==> [Propellor Shaft]

This arrangement provides multiple advantages:

1. There is no clutch to be engaged or to break down. A clutch would have been needed when diving to disconnect the engines from the propellor shafts.
2. The engines can be run at a high speed for efficiency.
3. The engines can run at a consistent speed even when the propellors need to turn slowly.
4. It allows for four engines to be installed in two separate engine rooms.
5. Four engines can provide a higher maximum speed for a larger submarine.
6. Any combination of engines can be used depending on power requirements.
7. The batteries can be recharged on a circuit separate from the one operating the boat.

At this point, we had a workable design for a long-range submarine with space for sufficient fuel and weapons. It was also large enough to provide some measure of habitability for the crew. This is what we built just before and during WW2.