(continued from KTB #111)

PRE-WORLD WAR II BUILDUP

On 19 July 1940, following the fall of France, Congress passed the Two Ocean Navy Act, which authorized the construction of 70,000 tons of submarines. So now the Navy had the organizational structure, the funds and the submarine design needed to go into mass production. As an example of mass production, it took only 317 days to build USS CORVINA (SS 226) from keel-laying to commissioning in August 1943.

In December 1940, the Navy began a series of controlled depth charge tests against the newly built USS TAMBOR (SS 198). Three hundred pounds of TNT were set off at distances from the hull ranging from 500 yards to less than 100 feet. The tests were repeated again in 1944 at distances as close as 75 feet. These tests resulted in a long list of improvements, which helped our submarines survive depth charge attacks. It was estimated that some depth charges or bombs exploded as close as 15 feet from the hull during the war - yet the submarine survived.

A strong gun foundation, both fore and aft of the conning tower, was added even though a good 'wet' 5" gun was not available until well into the War.

DEVELOPMENTS DURING WORLD WAR II

As can be expected, the War produced numerous small improvements and innovations like hydraulic mechanisms for operating the torpedo tube outer doors, washing machines and ice-cream makers. Some more important improvements included more powerful diesel engines - the engines from General Motors produced 1,600 BHP at 750 rpm and resulted in a two-knot increase in speed. Many boats were re-engined with this engine during the War. Then there was the 'pencil' type attack periscope, which was made as small as possible to minimize surface exposure, plus it was operated by a new hydraulic hoist. Two more forward torpedo tubes were quickly added at the beginning of the War, bringing the total to six.

Because of the success of a weight saving and simplification program, it was necessary to add a substantial amount of lead ballast to obtain proper trim. However, it didn't take long to realize that this amount of added weight could be better used in a thicker pressure hull of 7/8 inch rather than 9/16 inch thick. And not just one using the normal mild steel hull material, but one using a new high tensile steel (HTS) which was a chrome-vanadium steel alloy with a yield strength of 50,000 PSI. With a 7/8 inch steel plate, the hull had a collapse depth of 925 feet. These pressure hulls were ring-stiffened circular cylinders with hemispherical end caps. This new hull so impressed Admiral McKee that he was confident the hull could withstand the pressure depth of 600 feet. He even expressed his confidence in the new hull design to the new PCO's (Prospective Commanding Officers) of the BALAO Class. He said that their ships were safe down to 600 feet, but to provide the necessary safety margin the new BALAO Class would have an operating depth of 400 feet. This hull was one of the most significant technical improvements developed during the War. It offered several important advantages. Initial detection of the submarine at deep depths was more difficult. Depth charges took longer to reach these depths, giving the submarine more time to escape. The hull also provided more ability to withstand depth charge attacks in shallow waters. In addition to producing a stronger pressure hull, another benefit from the simplification program was to reduce the number of hull openings and electrical hull fittings.

Other Improvements During the War Include:

1. Radio. The standard long-range fleet communication was VHF and then UHF. However, in 1930 and then again in 1941, radio communication tests were made using very low frequency (VLF) which could be detected by a submerged submarine operating at periscope depth. A special loop antenna (initially a radio direction finder) was mounted near the top of the periscope supports following the 1941 tests which allowed the submerged submarine to receive the VLF radio broadcasts. An even lower frequency system, called Extremely Low Frequency (ELF) was used at any submarine depth as a 'bell ringer' to tell the submarine to come up for a message. ELF was not good for much else since at its low frequency (30 - 300 Hz) it could not contain much data.

2. Sonar. Regardless of what is said about Sonar, it was the periscope that was the principal sensor throughout World War II. To maximize the depth of the submarine during periscope operations, the periscope eyepiece was placed above the main pressure hull in a conning tower with other equipment necessary to determine the fire-control solution. However, sonar and acoustics were soon to elevate target sensing into an art all to itself.

In 1941 the WDA sonar set went into production. This was a crude active echo-ranging and listening system with the sound head mounted on a shaft that retracted into a special trunk below the forward torpedo room. This was called a 'searchlight' sonar since the piezoelectric transducer was rotated to get a bearing. The operating frequency was 25kHz and a range of 1,500 yards was typical. During the War this was replaced with the JT which operated at a lower frequency to increase its range.

A passive listening sonar system (called JP or JK) was installed in 1942 consisting of two hydrophones on a "T" shaped pole mounted over the forward torpedo room and trained manually from below. This device provided the bearing of the incoming sound signal.

By 1944 a short range, frequency modulated (FM) active sonar set (called QLA) was developed to allow the submarine to pick its way through a minefield.

This paper will continue on KTB #113 next month, and we will begin with developments in submarine-mounted radar.

More U.S. Submarines: A Technical History

S-Class (#111)
Pre-WWII Build-up and WWII Developments (#112)
Radar and Countermeasures (#113)
Post WWII Period (#114)
Missiles, Subs, and the USS Albacore (#115)
Early Nuclear Propulsion (#116)
Boomers and Fast Attack Submarines (#117)
Polaris and Other Missiles (#118)
Trident Missiles and Attack Subs (#119)