How does a 1,600-ton conventional submarine get through the protection of a floating airbase? The U.S. Navy drills in 2005 with the participation of the Swedish HSwMS Gotland and the carrier USS Ronald Reagan are still painful to the professional world as the result negated the institutions intuition. A carrier strike force is formed with layers of protection, like escorting cruisers, destroyers, aircraft, helicopters and, typically, an attack submarine, to ensure an effective range of the weapons stays out of reach. However, in one of the most famous runs, Gotland got into place and made a fake torpedo strike, which was counted as a “hit” according to the rules of the exercise. There were no accidents to any ship, but the incident caused a hard engineering truth to be recognized: undersea superiority may not be as much size as it is signatures.
Air-independent propulsion (AIP) and the resulting tactical discipline was the advantage of Gotland. Diesel-electric boats with AIP can spend more time on the water without snorkeling, which drastically decreases exposure time and the noise produced by running diesels. A submarine with battery power may be underwater and produce sound of acoustic levels lower than those of the ocean itself, including waves, biologics, commercial traffic, and stratified thermal effects that bend sound in complicated patterns. A sonar operator under such conditions is not hearing a submarine; rather, he is seeking statistical abnormalities in a moving noisy baseline. Anti-submarine war during the Cold War was designed to respond to superficial and faster nuclear submarines and the exercise pointed out how such supposition could be incorrect with modern conventional warships, particularly in shallow or coastal waters where bottom bounce, temperature variation, and dense civil presence adversely affects the detection ranges and the classification of assurance. This exercise was significant both in what it revealed at the organizational level and in what it revealed at the technical level.
Submarine carrier defense is a geometrical problem. The screening forces need to keep a perimeter that is sufficiently wide to drive the unwanted submarines beyond the torpedo range, though constantly updating pictures of contacts that are always suspect. Dipping-sonar helicopters can be used to survey a region very quickly, although they are sensitive to cueing, sortie generation and the sea state in which they have to operate. Surface vessels may tow arrays and follow active or passive search patterns, although towing geometry, self-noise and the acoustic environment may create gaps. A silent submarine need not be omnipresent, it need only have one passage along which the screen is thinned, the environment is disguised or the defenders are in a position of necessity. Gotland capitalized on such seams in the course of training where he found the space of quiet so that detection lagged slower than the decision making pace.
The technical design considerations can be used to understand why this type of submarine was such a handy sparring companion. The Gotland class used a Stirling-based AIP system and additional signature-management techniques found in open literature, such as a Stirling engine that would charge a 75-kilowatt battery and other characteristics designed to make the ship less detectable to magnetic, radar and sonar sensors. What was to be invisibility was time more time to be underwater, more freedom in approach patterns and less time when the submarine was forced to take more risk to recharge or ventilate. Time is a weapon in a competition where detection is needed before the engagement is made within minutes or hours.
The aftereffects were drawn towards two parallel issues of modernization. To start with, sensors and training had to be compatible with the quiet-diesel problem set, not just the high-speed nuclear one in littorals, in particular. Second, even when a submarine gets into firing range, the anti-torpedo arsenal was still lopsided, in contrast to anti-missile. Test programs include the carrier-fitted Anti-Torpedo Device System (ATTDS) that demonstrated the attractiveness of hard-destructive intercepts, but also demonstrated how hard it is to develop effective, low-false-alarm automation in a congested maritime environment. The Gotland exercise lasts so long because it binds these threads together: stealth is not a technology, but a regime of propulsion, signatures, ocean physics, and how the defender can convert uncertain data into timely action.
