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USS Platte (AO 186) on 15 December 1982 during sea trials.

USS Platte (AO 186) on 15 December 1982 during sea trials.
Click on this photograph for links to larger images of this class.

Class: CIMARRON (AO 177)
Design: SAIP Project 739.75
Displacement (tons): 8,210 light, 27,500 full
Same, jumboized: 11,645 light, 36,977 full
Dimensions (feet): 591.3' oa x 88' e x 33.5' mean
Same, jumboized: 700' oa, 661' wl x 86' wl, 88' e x 32' max nav
Armament: Space and weight for 2 CIWS, these were in AO 180 and 186 by 1983-84 and in 179 by 1991. No additional armament specified for Jumbo
Accommodations: 12 officers and 148 enlisted, accommodations for 221 personnel (246 as jumboized)
Speed (kts.): 20 originally, 19.4 and 19.0 sustained as jumboized
Propulsion (HP): 24,000
Machinery: Steam geared turbines, 2 boilers (600psi), 1 screw

177CIMARRON9 Aug 1976Avondale18 May 197828 Apr 197910 Jan 1981
178MONONGAHELA9 Aug 1976Avondale15 Aug 19784 Aug 19795 Sep 1981
179MERRIMACK25 Jan 1977Avondale16 Jul 197917 May 198014 Nov 1981
180WILLAMETTE11 Apr 1978Avondale4 Aug 198018 Jul 198118 Dec 1982
186PLATTE11 Apr 1978Avondale2 Feb 198130 Jan 198216 Apr 1983

AONameTDecommStrikeDisposalFateMA Sale/Depart
177CIMARRON15 Dec 19983 May 199928 Jul 2001MA/T7 Nov 2012/D
178MONONGAHELA30 Sep 199930 Sep 199929 Nov 2001MA/T30 Jan 2015
179MERRIMACK18 Dec 199818 Dec 199829 Nov 2001MA/T21 May 2013/D
180WILLAMETTE30 Apr 199930 Apr 199928 Jul 2001MA/T26 Nov 2013/D
186PLATTE30 Jun 199930 Jun 199929 Nov 2001MA/T4 Nov 2014/D

Class Notes:
By the early 1970s the concept of mobile logistic support for carrier groups centered on AOEs was accepted doctrine but the Navy had only four AOE 1 class ships that were fully capable of meeting it. To fill the gap it had to rely on the AOR 1 and jumboized AO 51 types which were considerably smaller, slower, and had less capacity for ammunition. Vietnam-era fiscal constraints prevented resolution of the problem, and in 1973 a design for a new class of oiler was produced that except for speed was extremely austere. The proposed ships were significantly smaller than the NEOSHO class of the 1950s and were the only non-wartime AOs built with single screws. They had only the UNREP capability of the World War II AO 22 class. They were designed to provide two complete refuelings to a conventional aircraft carrier (CV) and its six to eight accompanying escort ships, were navy-manned, and were designed for operation with the smallest possible crews. Automation of the main propulsion and auxiliary equipment, replenishment stations, cargo handling equipment, etc., was incorporated into their design. Propulsion was by a single screw plant of 24,000 SHP at full power that included two boilers, a cross compound main propulsion turbine, and a double reduction gear. A proposal to give the ships a miniature multi-product capability by lengthening them to add cargo holds for ammunition and stores was endorsed by COMPACFLT but rejected by CNO's office. Construction of the class became possible after the House Armed Services Subcommittee recommended in 1975 that Congress adopt a thirty-five ship per year shipbuilding program over a five year period. The first ships of the class were funded in FY 1976, the request for FY 1975 funding having been rejected by Congress. Approved characteristics for the FY 1975 Fleet Oiler (AO), SAIP Project No. 739.75, were promulgated on 14 November 1973 and updated for the AO 177 class on 27 August 1979 with a single change on 9 October 1981.

All five ships were jumboized at Avondale between March 1989 and September 1992. Top Level Requirements were promulgated for an oil only variant of the AO 177 (Jumbo) class fleet oiler on 17 March 1987 and for an ammunition variant, to which all of the ships were converted, on 5 February 1988. (Top Level Requirements (TLR), which were not numbered, replaced the earlier numbered Ships Characteristics Board (SCB) projects as a means of defining the characteristics of new designs.) The Top Level Requirements for the AO-177 (Jumbo) established the requirements for the design and construction of the mid-bodies and new equipment to be added to the existing AO 177 class ships. Congressional action on the FY 1987 budget mandated that the Navy jumboize the AO 177 class to the original 180,000 barrel oil only variant and authorized $40 million for the FY 1987 lead ship, which was to enter service in November 1989. The program was evidently slipped to FY 1988, however, and a CNO memo of 15 January 1986 authorized proceeding with the ammunition variant, setting a cost cap of $63.3 million for the alteration and specifiying that the FY 1988 ammunition variant conversion would enter service in January 1991. MERRIMACK beat this date by a month.

The objective of the AO 177 class jumboization program was to acquire through the addition of mid-sections to the five existing AO 177 class ships replenishment shuttle ships capable of the rapid transfer of POL to battle group replenishment ships (AOE, AOR, and AO) by means of vertical and connected (traditional) replenishment (VERTREP and CONREP) at sea. In the absence of a battle group station ship the AO 177 (Jumbo) would be capable of operation with the battle group as an attrition filler. The design incorporated the addition of a 109-foot parallel mid-body, providing for an increase in POL capacity from 120,000 to 180,000 barrels in the original oil only variant. The jumboized ships also incorporated a second Fairbanks Morse emergency diesel generator, additional air conditioning capabilities, several cargo holds, additional crew berthing (25 men), two "Standard Tensioned Replenishment Alongside Method" (STREAM) cargo stations to transfer ammunition and stores while fueling, which replaced the two original non-tensioned cargo stations, and tiedowns for 21 cargo containers including 3 refrigerated. The existing rudder was slightly enlarged and a new propeller was designed to maintain the maneuvering capability and powering performance of the ships at 19 knots sustained speed. In the ammunition variant POL capacity was reduced to a minimum of 150,000 barrels (reducing mean draft from 33.5' to 31.5' and full load displacement from 37,550 to 34,800 tons) in exchange for stowage for 625 tons of conventional weapons or additional non-refrigerated break-bulk cargo on three levels and a 25 x 6.5-foot elevator to serve all three levels of the hold, the main deck, and the 01 level. It was later estimated that the jumboization increased crew requirements by about 15 persons.

To save expenses and in keeping with the Navy's move away from steam propulsion the class was soon replaced by the diesel-powered HENRY J KAISER class replenishment oilers, and the jumboized AO 177 class ships lasted only about eight years before leaving service. WILLAMETTE, replaced by USNS JOHN ERICSSON (T-AO 194), was the last non-nuclear steam-propelled warship home ported in Pearl Harbor.

Ship Notes:
177CIMARRONFY 1976. Jumboized Jun 1990-Mar 1992. To MA custody 9 Feb 1999. Departed NDRF 7 Nov 2012 under domestic sale.
178MONONGAHELAFY 1976. Jumboized Jan 1990-Oct 1991. To MA custody 22 Jun 1999. Departed NDRF 13 Mar 2015 under domestic sale.
179MERRIMACKFY 1977. Jumboized Mar 1989-Dec 1990. To MA custody 21 Dec 1998 on long-term layup pending a transfer to Brazil that did not materialize. Departed NDRF 21 May 2013 under domestic sale.
180WILLAMETTEFY 1978. Jumboized Oct 1989-May 1991. To MA custody 22 Jun 1999. Departed NDRF 26 Nov 2013 under domestic sale.
186PLATTEFY 1978. Jumboized Nov 1990-Sep 1992. To MA custody 14 Jul 1999. Departed NDRF 4 Nov 2014 under domestic sale.

Page Notes:
Compiled: 18 Sep 2021
© Stephen S. Roberts, 2021
Special sources: Thomas Wildenberg, Gray Steel and Black Oil (Annapolis, 1996)