Arleigh Burke class

The Arleigh Burke class represents the first class of destroyers of the US Navy built around the AEGIS Combat System, based on the multifunction phased-array radar SPY-1D. This class is also one of the most numerous to ever serve in the US Navy, with 62 exemplars completed. After the decommissioning of the last unit of the Spruance class in 2005, those of the Arleigh Burke class became the only active destroyers in the US Navy. They are classified as guided-missile destroyers (DDG) and are fitted with integral protection for nuclear, biological and chemical warfare.

With a total length of 155 meters, a beam of 20 meters, a draft of 9.3 meters and a full load displacement of 9200 tonnes, these ships are larger and more heavily armed than previous guided-missile destroyers. A novelty in the design of the structure was the profusion of sloped surfaces to improve stealth capability. Another particularity of the project is the integral construction in steel, unlike the previous approach of building the hull in steel and the superstructure in aluminum, lighter but more vulnerable to cracks and fires.

The propulsion plant comprises four gas turbines General Electric LM2500 that give a total output of 108000 shaft horsepower, coupled to two shafts, each one driving a five-bladed propeller, reversible and of variable pitch. Top speed can exceed 30 knots and operational range is around 4400 nautical miles (8100 kilometers) at a cruise speed of 20 knots. The complement is around 320 people, slightly lesser than in the preceding Spruance class.

The armament includes two spots for the Mk 41 VLS, which can fire several types of surface-to-surface and surface-to-air missiles, with a total of 96 cells, 64 astern and 32 at prow, as it can be clearly seen in the second photograph below. A picture on the left bar shows an 8-cell module of this system and three types of missiles that it can launch.

Arleigh Burke class missile destroyer (early version)
Arleigh Burke class missile destroyer (early version)
Other armament includes four RGM-84 Harpoon antiship cruise missiles (in the early version only), one Mk 45 127-millimeter cannon, one Mk 15 Vulcan Phalanx CIWS 20-millimeter cannon (two in the early version), two Mk 38 25-millimeter cannons and two Mk 32 triple launchers for Mk 46 324-millimeter antisubmarine torpedoes. The early version of the Arleigh Burke class lacked hangar, an unfortunate decision that was rectified in the newer version IIA, which includes hangar facilities for two MH-60R Seahawk helicopters with LAMPS III equipment installed, as it can be seen in the photograph below.

Arleigh Burke class missile destroyer (late version)
Below, a Mark 45 cannon performing automatic fire onboard an Arleigh Burke class destroyer. Note the turret built with flat surfaces to reduce radar signature, different to that built with rounded surfaces. The 127-millimeter ammunitions can hit targets up to 50 kilometers afar, but to achieve this it would be necessary to use guidance elements for the terminal flight phase.

Mk 45 127-millimeter cannon
Below, a beautiful picture of the DDG-88 USS Preble, delivered to the United States Navy in November 2002.

Arleigh Burke class missile destroyer USS Preble

Spruance class

The Spruance class of antisubmarine destroyers was developed to replace a large number of obsolete destroyers that had been built during World War Two and modernized in the 1960s. In service for three decades, the Spruance class was designed to escort a carrier group with a primary antisubmarine mission. The first unit was commissioned in 1975, causing an initial controversy, specially among members of the United States Congress, who believed that the simplistic looks of the ship, with few visible weapon systems, implied weakness in comparison with the imposing Soviet counterparts, which had much more evident armament.

But despite the criticism, this was a powerful design for the intended antisubmarine role: the USS Spruance hid much "state of the art" equipment and all-digital weapon systems inside her bulky structures. The ship was equipped with the advanced bow sonar SQS-53 which could work in multiple active and passive modes, the towed sonar SQR-19 and acoustic decoys Nixie SQL-25 to deceive incoming torpedoes. The adoption of gas turbines as propulsion plant, chosen due to their easy maintenance and low manpower demand, granted as well a notable reduction in underwater noise emissions, allowing for very silent antisubmarine operations.

The magazine of the octuple ASROC launcher could store not less than 24 reloads and sliding doors at each side of the flight deck hid two triple torpedo launchers Mk 32. Besides, the large hangar behind the funnel, of about 100 square meters, could house two LAMPS helicopters. Two Mk 45 127-millimeter cannons in single mounting (an automatic and dual purpose weapon, recently introduced then) completed the armament.

Spruance class antisubmarine destroyer (early version)
The Spruance class was further upgraded in the 1990s with the Mk 41 VLS, allowing to launch the surface-to-surface missile Tomahawk, being reclassified the modernized vessels as guided-missile destroyers (DDG); they had been classified until then as conventional destroyers (DD). However the Spruance class lacked the capabilities of later AEGIS destroyers and stealth design was inexistent, with all-vertical surfaces. So, even if the Spruance was a costly project and advanced technologies were specifically developed for it, the US Navy preferred to accelerate its retirement. The last ship of the class was decommissioned in 2005, with the largest part of the 31 units completed being scrapped or used as targets.

The Spruance class was comparable in size to cruisers (CG) under the US Navy's hull classification symbol system. Total length reached 172 meters, beam was 16.8 meters and draft was 8.8 meters, while full load displacement reached 8040 tonnes. The destroyers of the Spruance class were the first large ships operated by the US Navy that used propulsion by gas turbines (four General Electric LM2500), which generated about 80000 shaft horsepower actuating in two shafts. Top speed reached 32.5 knots and operational range was around 6000 nautical miles (11000 kilometers) at 20 knots, being decreased to about a half if navigating at 30 knots. The complement was around 335.

Air defense was originally entrusted to one Raytheon GMLS Mk 29 octuple launcher for the short-range surface-to-air missile Sea Sparrow; later two Mk 15 Vulcan Phalanx CIWS 20-millimeter cannons were added. The armament, logically, was upgraded during the service lifetime. Two quadruple canisters for the antiship missile RGM-84 Harpoon were added and, in some ships of the class, two quadruple launchers ABL Mk 43 for the surface-to-surface cruise missile Tomahawk and one 21-cell launcher for the short-range surface-to-air missile RIM-116 (Rolling Airframe Missile) were installed.

Above the hangar was placed the Raytheon Mk 91 director/illuminator for the Sea Sparrow, a radar in bands I/J formed by two different antennas, of which one is receiver and the other is transmitter.

Mk 91 fire control radar
Before being equipped with VLS, the destroyers of the Spruance class had an octuple ASROC launcher at prow and, from October 1982, some of them were equipped with two quadruple launchers ABL Mk 43 for the surface-to-surface missile Tomahawk.

ABL Mk 43 missile launcher
In the late 1980s, in twenty-four of the ships of the class both the ASROC and ABL launchers were replaced by one 61-cell Mk 41 VLS which could launch both Tomahawk and ASROC missiles. The large hangar remained always operative, housing two Sikorsky SH-60 Seahawk LAMPS III helicopters, introduced around 1980. The modernized version of the Spruance class can be seen in the photographs below; note the launcher for RIM-116 in the starboard corner astern.

Spruance class missile destroyer (late version)
Spruance class missile destroyer (late version)
The electronic equipment included, in the fore mast, the fire control radars Lockheed SPQ-9A (in a dome) and SPG-60 and the surface search radar ISC Cardion SPS-55, all of them in bands I/J. Next to the fore stack there was an early-warning device Raytheon SQL-32. The aft mast housed the air search radar Lockheed SPS-40B/C/D, placed on top, and the Hughes Mk 23 TAS (Target Acquisition System), operating in band D, able to automatically react against sea-skimming missiles at distances up to 185 kilometers, placed in the lower platform.

Some of the ships were fitted with infrared tracking sensors astern to allow them to operate in a very tight formation during night.

Infrared tracking sensor

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