SSBN-608 Ethan Allen-Class FBM Submarines

Because the first five U.S. SSBNs were actually built as a variant of the earlier USS Skipjack (SSN-585) configuration, Ethan Allen was the first submarine specifically designed for the strategic SSBN role. Ethan Allen class (SSBN-608) FBM Submarines were larger than the George Washingtons, incorporating the hull features of the Thresher/Permit class with a test depth of 1,300 feet. Their deeper diving capabilities were developed at Carderock, DTMB, and EES. These 7,800-ton boats (GW class was 6,700 tons) had only four torpedo tubes compared with GW's six. They also had Thresher-type machinery and quieting.

The Polaris SLBM was a revolutionary weapon system. First, Polaris incorporated major technical advances with respect to submarines and missiles. Also significant was the almost unprecedented growth potential of the system; essentially the same submarine types carried each new generation of missile-from Polaris A-1 to the A-2, A-3, Poseidon, and Trident I missiles. There were in fact three distinct classes of Polaris submarines:

1. 5 SSBN-598 George Washington class
2. 5 SSBN-608 Ethan Allen class
3. 31 SSBN-616 Lafayette class

There were significant improvements in each succeeding class, with the Lafayette having two subtypes (based primarily on engineering changes). However, all three classes had the same basic configuration, the same S5W reactor plant, and carried 16 missiles. The early five boats of the George Washington class with their 382-foot lengths and 6700-ton displacements carry the A-3 Polaris now. The boats of the 410-foot, 7900-ton Ethan Allen class also launch the A-3. The Poseidon-carrying boats consist of 31 Lafayette-class submarines with their 425-foot lengths and 8250-ton displacements.

The United States has had an operational SLBM force since November 1960, when the first Polaris-carrying submarine, the U.S.S. George Washington, put out to sea on patrol This was five years after the first U.S. nuclear submarine, the Nautilus, was launched. This five-year period was needed to develop a solid propellant missile system to launch an SLBM from a submerged submarine. The first successful underwater launch of a Polaris missile occurred in July 1960, again from the Washington. A total of five submarines were fitted with the 1200 nautical-mile-range A-1 Polaris missiles. To improve the capability of the Fleet Ballistic Missile (FBM) force, the 1500 nautical-mile-range A-2 Polaris was developed. The A-2 was first launched from the U.S.S. Ethan Allen off the Florida coast in October 1961.

The submarines were powered by steam turbines that get their energy from water-cooled nuclear reactors. With an atmospheric control system of immense capacity, the submarine did not even have to raise a snorkel to obtain air. If it were not for the needs and endurance of the human crew, these submarines could stay on station almost indefinitely. Each submarine carried a crew of 12 to 14 officers and about 130 enlisted personnel, and each has two crews, a Gold and a Blue one. While one crew was on patrol, the other is in port training, orienting new crew members, taking leave, and in general getting ready for the next cruise. Normally, the submarines are on station for sixty-day periods.

The Polaris and Poseidon missiles were launched from the submarine's 16 tubes while the craft is submerged and out of sight. The missile is ejected from the tube either by compressed air or by a gas and steam generator system. Once the missile reaches the water's surface, the first stage of the missile is ignited and sent on its way. There is access to each of the 16 independently controlled launch tubes even during patrol at sea for performing inspection and maintenance of the missiles. It should be noted that all Polaris submarines were fitted with launch tubes that were much larger in diameter than the original missile, which permitted the use of larger and more advanced missiles as they were developed over the years. A total of 33 boats were equipped with the A-3, including the original five A-1 carrying boats which were refitted with the A-3. SSBN-608 Ethan Allen-Class carried the Polaris A-1, A-2, and A-3 strategic ballistic missiles at various stages of her career.

Ethan Allen (SSBN-608), operating in the Pacific as part of Joint Task Force 8 in Operation Frigate-Bird, fired the only nuclear-armed Polaris missile ever launched on 6 May 1962. The Polaris A1 missile was launched while the Ethan Allen was submerged in the Pacific, and its nuclear warhead was detonated over the South Pacific at the end of its programmed flight. The shot was made during the 1962 atomic tests. Subsequent analysis of the recorded data and cloud samples taken by Air Force B-57 Canberra aircraft revealed that the air burst took place 1.25 miles from the nominal aim point and that the Polaris W-47 thermo-nuclear warhead performed up to expectations, with a yield in the 600-kiloton range.

To date, this is the only complete proof test of a U.S. strategic missile. Because of the ban on atmospheric testing, similar tests are unlikely. Of the three components of the Triad, the land-based ICBMs were the only force that was not extensively tested. Bombers regularly took off, flew missions, and dropped bombs; prior to test-ban agreements, bombers dropped nuclear weapons (and dummy bombs) in full-system tests. Similarly, submarines regularly fired unarmed ballistic missiles-sans warheads-on test ranges. But no nuclear-armed ICBM has been launched from an operational silo. Periodically, the silo crews fired various ICBMs from test facilities at the Vandenberg Air Force Base in California and from Cape Kennedy in Florida under highly controlled conditions. But even periodic efforts to launch an ICBM with reduced fuel and no warhead from an operational silo have failed, and Congress has refused approval of full-range test firings from an operational silo that would take even an unarmed missile over urban areas. After returning to the Atlantic from Operation Dominic, Ethan Allen commenced her first deterrent patrol in late June 1962 and eventually completed 57 deterrent patrols before conversion to an SSN in September 1980. The ship was decommissioned in March 1983 and spent her final years at the Puget Sound Naval Shipyard, where her dismantling and nuclear recycling were completed in July 1999.

John Marshall (SSBN-611) became the last submarine to give up her Polaris A2s for Polaris A3 capability when she went into overhaul on 1 November 1974. Some of these submarines were later reclassified as attack submarines under the Strategic Arms Limitation Treaty (SALT) agreements. The boats were decommissioned in 1983 (two boats), 1985, 1991, and 1992.

Historic Context Statement-The United States Navy in the Cold War 337 TABLE II-26 ETHAN ALLEN CLASS SUBMARINES NAME NUMBER BUILDER BASE ORDERED COMMISSIONED DECOMMISSIONED Ethan Allen SSBN-608 Electric Boat varied 7/17/1958 8/8/1961 3/31/1983 Sam Houston SSBN-609 Newport News varied 7/1/1959 3/6/1962 9/6/1991 Thomas A. Edison SSBN-610 Electric Boat varied 7/1/1959 3/10/1962 11/30/1983 John Marshall SSBN-611 Newport News varied 7/1/1959 5/21/1962 7/22/1992 Thomas Jefferson SSBN-618 Newport News varied 7/22/1960 1/4/1963 1/24/1985