The Navy procured 18 Ohio (SSBN-726) class nuclear-powered ballistic missile submarines (SSBNs) between FY1974 and FY1991 to serve as part of the U.S. strategic nuclear deterrent force. They are commonly called Trident submarines because they carry Trident submarine-launched ballistic missiles (SLBMs). The first Trident entered service in 1981, the 18 th in 1997. The first 8 (SSBNs 726 through 733) were originally armed with Trident I (C4) SLBMs; the final 10 (SSBNs 734 through 743) were armed with larger and more powerful Trident II (D5) SLBMs. The boats were originally designed for a 30-year life but were later certified for a 42-year life, composed of 20 years of operation, a two-year mid-life nuclear refueling overhaul, and then another 20 years of operation. The Clinton Administration's 1994 Nuclear Posture Review (NPR) recommended a strategic nuclear force for the START II strategic nuclear arms reduction treaty that included 14 Tridents (all armed with D5 missiles) rather than 18. This recommendation prompted interest in Congress and elsewhere in the idea of converting the first 4 Trident SSBNs (SSBNs 726 through 729) into non-strategic submarines called SSGNs, so as to make good use of the 20 years of potential operational life remaining in these four boats and bolster the U.S. attack submarine (SSN) fleet, which has been significantly reduced in recent years. The Bush Administration's 2002 NPR retained the idea of reducing the Trident SSBN force to 14 boats. Some observers supported the SSGN conversion concept while a few others questioned it. The Navy in the late 1990s generally supported the concept in principle but also expressed concern over its ability to finance all four conversions while also funding other priorities. Congress, as part of its action on the proposed FY1999 defense budget, directed the Secretary of Defense to report on the issue to the congressional defense committees by March 1, 1999. The report was delivered to Congress in classified and unclassified form in June 1999. The Bush Administration highlighted the program as an example of defense transformation. The Bush administration, in its amended FY2002 defense budget submitted to Congress in June 2001, requested funding to begin the refueling and conversion of SSBNs 727 and 729, and additional funding to begin the inactivation and dismantlement of SSBNs 726 and 728. Since the Bush administration, prior to submitting this budget, had highlighted the Trident SSGN concept as an example of defense transformation, it came as somewhat of a surprise, particularly to supporters of the SSGN concept, that the Bush Administration requested funding to convert only two of the four Tridents. Navy officials said the decision was driven in part by Navy budget constraints, and that the deadline for committing to the refueling and conversion of SSBNs 726 and 728 on a timely basis had passed some time between late 2000 and June 2001. This also came as a surprise to some observers, since the Navy during the intervening months had not done much to publicize the impending deadline. The Navy later explained, however, that refueling and converting SSBNs 726 and 728 would still be possible if funds were provided in FY2002, though the schedule for planning and carrying out the operation would now be less than optimal. Congress, in marking up the FY2002 budget, increased funding for the program to the level the Navy said was needed to support a four-boat conversion program. The Bush Administration subsequently pursued the program as a four-boat effort. The Tridents as converted can carry up to 154 Tomahawk cruise missiles (or other non-strategic land attack missiles ) and 66 Navy SEAL special operations forces (SOF) personnel. Each boat retains its 24 large-diameter SLBM launch tubes but the boats have been modified as follows: SLBM tubes 1 and 2 were altered to serve as lockout chambers for the SOF personnel. Each chamber is equipped to connect to an Advanced SEAL Delivery System (ASDS) or Dry Deck Shelter (DDS). Other spaces were converted to berth and support 66 SOF personnel. Tubes 3 through 24 were modified to carry 7 Tomahawks each, for a total of 154 Tomahawks. Alternatively, tubes 3 through 10 can be used to carry additional SOF equipment and supplies; leaving tubes 11 through 24 to carry 98 missiles. The Trident SLBM fire control systems were replaced with tactical missile fire control systems, and certain other systems aboard the boats were modernized. In addition to these changes, each boat underwent a mid-life engineering (nuclear) refueling overhaul (ERO). Without EROs, the boats would have exhausted their nuclear fuel cores and been inactivated in the FY2003-FY2005 time frame. Each SSGN is to deploy for a period of more than a year, during which time it is to be operated by dual (Blue and Gold) crews rotating on and off the ship every three or four months. The aim is to have two of the four SSGNs continuously forward deployed until the ships are decommissioned in the late 2020s. As of September 30, 2007, SSBNs 726 and 727 were homeported in Puget Sound at Bangor, WA, while SSBNs 728 and 729 were homeported at Kings Bay, GA. The report of the 2001 Quadrennial Defense Review, submitted to Congress in September 2001, directed the Secretary of the Navy to explore options for homeporting SSGNs in the Western Pacific. SSBNs 726 and 727, though homeported at Bangor, are operated out of the U.S. territory of Guam in the Western Pacific. The SSGNs are to operate as covert platforms for conducting strike (i.e., land attack) and SOF-support missions. In the covert strike role, the boats can fulfill a substantial portion of the in-theater Tomahawk missile requirements that are established by regional U.S. military commanders, and thereby permit forward-deployed multimission Navy surface combatants and SSNs to concentrate on other missions. In their SOF-support role, the SSGNs can be viewed as functional replacements for the James K. Polk (SSN-645) and the Kamehameha (SSBN-642)âtwo older-generation SSBNs that were converted into SSNs specifically for supporting larger numbers of SOF personnel. The Polk was retired in 1999 at age 33; the Kamehameha was retired in 2002 at age 36. The Bush Administration and other supporters of the Trident SSGN program highlighted the program as an example of defense transformation, citing the conversion of a strategic-nuclear-forces platform into a non-strategic platform, the large number of cruise missiles that an SSGN will carry (which is several times the number that can be carried by a standard Navy attack submarine), and the large payload volume of the boats for carrying future advanced payloads. Others observers demurred, arguing that Navy has converted older SSBNs into SOF-support submarines in the past, that the larger number of cruise missiles that the SSGNs carry is more of a quantitative difference than a qualitative one, and that funding the Trident SSGN program may actually have slowed the transformation of the Navy's submarine force by reducing the amount of funding available for research and development efforts supporting more radical and transformational changes to the Virginia-class attack submarine design. The submarine community intends to maximize the transformational value of the SSGNs by using them as at-sea test beds for new ideas, such as using submarines to deploy large-diameter, highly capable unmanned underwater vehicles (UUVs). Even if one judges the program not transformational, one might still judge it cost effective in terms of the capabilities it provides and in realizing a full, 42-year return on the original procurement cost of the boats. As shown in Table 1 , the Navy estimates the total cost for refueling and converting four Tridents (including both research and development as well as procurement costs) at about $4.0 billion, or about $1 billion per boat. This figure represents a substantial increase over earlier estimates for a four-boat program of about $2.4 billion in 1999-2000, and $3.3 billion to $3.5 billion in 2001-2002. Refueling and converting four Tridents avoids a near-term expenditure of about $440 million to inactivate and dismantle them. The estimated net near-term additional cost to the budget to convert the 4 boats rather than inactivate and dismantle them is thus $3.56 billion ($4.0 billion less $440 million), or about $890 million per boat. DOD estimated in 1999 that the operating and support (O&S) cost for two SSGNs over 20 years would be $1,645.3 million in constant FY1998 dollars, which equates to $1,777.9 million in constant FY2005 dollars, or an average of about $44.4 million per boat per year in constant FY2005 dollars. Using this figure, the total 20-year life-cycle cost for four Trident SSGNs (including research and development costs, annual operation and support costs, and eventual inactivation and dismantlement costs) would be roughly $7.6 billion in constant FY2005 dollars. All four Trident conversions have been completed, and Initial Operational Capability (IOC) for the program was declared on November 1, 2007. SSBN-726, the first ship to be converted, reportedly began its first operational deployment as an SSGN in October 2007.