(continued from KTB #118)

The current generation of FBM submarines are the OHIO class TRIDENT submarines. Their development began back in 1969 when the Secretary of Defense felt that because of projected Soviet advances in ASW our existing FBM fleet was too vulnerable. The issue laid dormant until 1972 when interest was again renewed, this time due to continued Soviet build up of their strategic defense forces. The TRIDENT program was to be a simultaneous effort to develop:

1. New long range improved missiles, designated C-4 and D-5.
2. A new quieter submarine to carry more than 16 D-5 missiles.

These longer range missiles with their improved accuracy, coupled with a submarine capable of quieter operations at higher speeds than the older boats, resulted in an enlargement of the patrol operating areas. This increased capability (coupled with a deeper diving depth) directly led to a decrease in Soviet ASW effectiveness and thus became the US Navy’s response to the increase in the Soviet threat. Many trade-offs for cost effectiveness were necessary, like the number of missiles per boat (24 rather than 16 as on older boats).

The new submarines could also take advantage of the new technologies available since the 1960’s and 1970’s such as noise reduction, crew habitability, new communications equipment, modular construction, and improved maintenance techniques.

The TRIDENT program was the first to feel the restrictions of the SALT and START arms reductions talks. However, it now appears that the eventual force level (18 to 24 TRIDENT SSBN’s) would be more of a budget issue than a response to any threat or the outcome of any arms reduction talks. As the OHIO class TRIDENT submarines began to be commissioned in the early 1980’s, the first ten POLARIS submarines were decommissioned and had their missile compartments deactivated.

Modern Attack Class Submarines

By the late 1950’s the Navy was ready to bring back the ALBACORE tear-drop hull together with nuclear propulsion to form a new attack submarine. The Navy started modestly with the 252 foot long USS SKIPJACK (SSN 585) and is currently building advanced versions of the 360 foot long USS LOS ANGELES (SSN 688). USS SKIPJACK was exceedingly fast, although limited to depths of World War II fleet boats, and was a lot noisier. Much of the subsequent submarine development efforts were directed towards quieting the propeller noise and machinery noise (very expensive), plus increasing the depth capability (with the usual electronic and acoustic upgrades along the way). A deep depth capability was necessary for several reasons:

To provide a maneuvering ‘cushion’ due to the faster speeds available;
to prevent excess propeller cavitation;
to improve the chance of evading ASW weapons;
to improve resistance to underwater explosions;
to avoid detection by hiding below the thermocline.

To obtain the deeper diving depths, HY-80 steel was used for the pressure hulls of the next generation of attack submarines; the THRESHER/PERMIT Class. USS SKIPJACK’s hull was based on USS ALBACORE, being shorter and fatter than the previous designs, resulting in three deck levels, This hull design was a return to a single-hulled submarine with the ballast tanks at each end of the pressure hull (hence, most of the pressure hull was also the outer skin of the submarine). The accompanying decrease in reserve buoyancy was not a problem since the submarine was to spend most of its time submerged. The sonar system grew extremely large, into a 15 foot sphere, in order to get the maximum range by utilizing the acoustic modes of propagation known as ‘bottom bounce’ and ‘convergence zone’. The sonar sphere allowed a passive sonar beam to be swept in both the vertical as well as horizontal directions. A low frequency, passive, towed array of sonar complimented the sonar system in the bow. The torpedo tubes had to be placed behind the sonar sphere where they were angled outboard about 10 degrees. In some newer boats additional launching tubes are installed vertically in the space behind the sonar sphere (but in front of the pressure hull) to fire TOMAHAWK missiles. the LOS ANGELES class is an attempt to retrieve the speed lost in the transition from the SKIPJACK to THRESHER to STURGEON classes and was justified in order to fulfill an old mission - direct task force support of the carrier battle group. Instead of anti-air (as in Radar Picket submarines) or anti-surface submarines, they are ASW submarines with their high submerged speed and long range sonar.

The SSN-21 (the lone SEA WOLF) may introduce yet another generation of fast attack submarines into the twenty-first century (but will be equipped with a few near-nineteenth century designed torpedo tubes).

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)