In 1982, after 31 ships were built, the class underwent a small redesign. The next eight, which formed the submarines' second flight, had 12 new vertical launch tubes that could fire Tomahawk missiles. The last 23 had a significant update with the 688i improvement program. These ships are quieter, with more advanced electronic components, sensors, and noise reduction technology. Dive planes are placed on the bow rather than on the sail and are retractable.
The Navy proposed four other ships, but later canceled them. In another test carried out in January in Boston Harbor, underwater communication was demonstrated for the first time by using a Morse code carrier to modulate the oscillator, thus demonstrating a means of acoustic communication between ships and submarines. The ships of the Hydrographic Office that carried out deep water surveys used sound depth devices of the Fessenden type, developed by the Submarine Signal Corporation. Data from a Fessenden underwater oscillator put into operation at the Nantucket Lighthouse in 1923 produced the data in the following table. In April 1918, a towed detector (OS) manufactured with the three microphones mounted in a four-foot equilateral triangle and the submarine hunter's engine turned off could detect a submarine moving at 4 or 5 knots over distances of 1 to 5 nautical miles.
When a drone flies over a specific area of a ship, such as the hull or rear, it transmits video to create a digital model of the ship that contributes to the detailed analysis of the ship, including potential areas of concern for corrosion or rust. Armen Kvryan, a doctor in principal materials engineering from the NSWC, has a doctorate in materials science and extensive experience in corrosion problems affecting combat systems thanks to his work in industry and academia. In addition to merchant ships and navies, fast passenger ferries operating from England to the coasts of Europe used submarine bells to check the positions of ships and, as early as 1930, they discovered the method of navigation used daily. At that time, General Electric was already doing some research for the Navy in the area of communications and submarine detection. World War I underwater detection efforts in the United States, Great Britain, and France provided the basis for several detection devices in the years after the war.
Quartz, Rochelle salt, and the magnetostrictive properties of ferrous materials, all investigated during the war, were available for use in transducers in post-war systems. With the tank secured against the side of the ship on the port side and the peak from bow to starboard, there was no need to drill a hole in the side of the ship. The growing naval interest in detecting submarines and the concern of commercial navigation to improve safety at sea through the use of underwater sound shared a common goal. Nowadays, scientists from Naval Surface Warfare Center (NSWC), Port Hueneme Division (NSWC PHD), and local companies are looking into using them to track corrosion or degradation of combat systems aboard Navy ships. Due to difficulties with sound transmission through air, sirens and fog horns were limited as warning devices for ships. In 1903, Submarine Signal Company's bells were installed for first time in Boston Harbor aboard Lightship 54. Towards end of 19th century people started developing commercial underwater sound devices to improve safety of merchant ships by alerting them about presence of rocky shores. The Naval Ship located in Pasadena has been equipped with special sensors and detection systems that allow it to detect submarines and other vessels at sea.
These sensors include acoustic detectors such as Fessenden Oscillators which can detect submarines up to 5 nautical miles away. Additionally, drones can be used to create digital models of ships which can be used to detect areas of corrosion or rust on board. Furthermore, quartz Rochelle salt and magnetostrictive properties can be used as transducers for underwater detection systems. The Naval Ship also has access to submarine bells which can be used to check positions of vessels at sea. This technology has been used since 1930 when General Electric began researching communications and submarine detection for Navy use.
Finally, sirens and fog horns are also used as warning devices for ships. In conclusion, Naval Ships have access to special sensors and detection systems which allow them to detect submarines and other vessels at sea. These sensors include acoustic detectors such as Fessenden Oscillators which can detect submarines up to 5 nautical miles away as well as drones which can create digital models of ships which can be used to detect areas of corrosion or rust on board. Additionally quartz Rochelle salt and magnetostrictive properties can be used as transducers for underwater detection systems while submarine bells can be used to check positions of vessels at sea.