Suamico-class oiler

	USS Cohocton
Class overview
Name	Suamico class
Builders	Sun Shipbuilding & Drydock, Chester, Pennsylvania; Marinship, Sausalito, California;
Operators	United States Navy
Preceded by	Kennebec class
Succeeded by	Neosho class
Subclasses	Escambia class; Cohocton class;
Built	1940–1945
In service	1942–1972
Planned	30
Completed	25 + 2 converted
Cancelled	3
General characteristics
Type	T2-SE-A1/2/3 tanker
Displacement	5,782 long tons (5,875 t) light; 21,880 long tons (22,231 t) full;
Length	523 ft 6 in (159.56 m)
Beam	68 ft (21 m)
Draft	30 ft 10 in (9.40 m)
Propulsion	Turbo-electric transmission, single screw, 6,000 shp (4,474 kW) (Suamicos); 10,000 shp (7,457 kW) (Escambias)
Speed	14 knots (26 km/h; 16 mph) (Suamicos); 15 knots (28 km/h; 17 mph) (Escambias)
Capacity	140,000 barrels (22,000 m3)
Complement	267 officers and enlisted
Armament	1 × 5-inch/38-caliber dual purpose gun; 4 × 3-inch/50-caliber guns; 4 × twin 40 mm guns; 4 × twin 20 mm guns;

The Suamico class were a class of 25 United States Navy oilers during World War II. Built to the Maritime Commission T2-SE-A1 (Suamico class), -A2 (Escambia class) and -A3 (Cohocton) designs, they used turbo-electric transmission, obviating the need for reduction gearing which was a major issue in US mass-production shipbuilding.

Construction

The Suamicos

Just before the war the United States Maritime Commission had developed a standardized tanker design, the T2, which could be mass-produced in time of war, and militarized as needed for naval auxiliaries. The T2 was given sufficient engine power to attain 16.5 knots (30.6 km/h), which the Navy considered the minimum required for a fleet oiler.

The T2 and its variants (see Kennebec-class oiler) however used conventional geared steam turbine propulsion, and with the massive expansion of US shipbuilding, a production bottleneck developed: the limited availability of the precision machinery needed to manufacture reduction gearing.^[1] The Sun Shipbuilding and Drydock Company of Chester, Pennsylvania worked around this problem by designing a T2 variant which used turbo-electric propulsion; that is, the steam turbine ran a generator, which in turn powered electric drive motors without the need for gearing.^[2] Compared to conventional geared turbines turbo-electric systems produced less power for the same size and weight, so Sun's T2-SE (steam-electric)-A1 design could only develop 6,000 shaft horsepower for 14 knots, but since commercial tankers typically only did 12–13 knots this was acceptable. Acknowledging the practicality of the design for merchant service, the Maritime Commission ordered 72 T2-SE-A1s from four shipyards in May 1941. Ultimately 536 T2-SEs would be built, the most-produced tanker design in history.

On 9 June 1942, Admiral Nimitz indicated an immediate need for four more fleet oilers. The War Shipping Board requisitioned the last remaining T2 and T2-A tankers still in commercial service, Catawba and Aekay, and, with reservations given their limited speed, two nearly-complete Sun T2-SE-A1s, Harlem Heights and Valley Forge. These were commissioned as USS Suamico (AO-49) and Tallulah (AO-50). In August, with the fourteen repeats of the big 18-knot (33 km/h) Cimarron class still a year from completion, the Navy took over the next two T2-SEs off Sun's ways, Oriskany and Stillwater, renamed Pecos (AO-65) and Cache (AO-67). On 7 August the Auxiliary Vessels Board recommended that the Navy add two oilers per month for a period of six months. While fifteen of the 15.3-knot T3-S-A1 type had been ordered by the Maritime Commission, only five (the Chiwawa class) would be completed in time, and so the Navy filled out the requirement with another seven T2-SE-A1s, AO-73 through 79, the first of which were acquired on the last day of 1942.

The Escambias

During the spring and summer of 1942, a period German U-boat captains called "the happy time," tankers were being sunk in the Atlantic faster than they could be built. In response, on 27 July the Maritime Commission decided that the new Marinship yard at Sausalito, California, created to produce Liberty ships, would construct T2-SE tankers instead, with an initial order of 22. However, there simply were not enough of the specified generator plants available. On the other hand, General Electric indicated its ability to provide the larger 10,000 hp (7,500 kW) turbo-electric plants designed for the P2-SE2-R1 Admiral-class fast transports, and Marinship's naval architects modified the original Sun design to make room for the larger installation. The Marin T2-SE-A2's engineering spaces were cramped, but it all fit; better yet, the new design was capable of speeds in excess of 15 knots (28 km/h). By the end of the year the Navy, unenthusiastic about the slower Suamicos, was eager to acquire the more powerful new version and requisitioned the first nine, which were launched starting in April 1943 and after conversion as fleet oilers started commissioning in October, as AO-80, USS Escambia, through AO-88.

The Maritime Commission followed its initial order of 22 T2-SE-A2s with another for 18 more; the Navy would acquire six of these as AO-91 through 96. By the time these started entering service in late 1944 the Navy was finding that fresh water was becoming more of a problem in the Pacific than fuel; accordingly Pasig and Abatan were converted to water-distilling ships (AW-3 and 4), and Soubarissen into a water tanker.

The A3s

On 16 October 1944 the Chief of Naval Operations recommended that the Maritime Commission building program for the last half of 1945 be modified to provide for the construction of nine additional oilers for the Navy. On 2 November 1944 the MC added to its program the construction of four ships at Marinship to the 10,000-horsepower T2-SE-A3 design together with five T3s at Bethlehem Steel. The T2-SE-A3 type was essentially an A2 built to Navy standards from the start rather than being modified later (converting a civilian tanker to a Navy fleet oiler represented an additional 4–6 months' work after delivery). The last three ships were completed without these features, after the Navy canceled them in the waning days of the war.

Postwar service

All of the oilers of the class were decommissioned to reserve in 1946; however all were reactivated for tanker duties with civilian crews by the Naval Transport Service and its successor the Military Sea Transportation Service in 1947–1950, except for Saranac, which had been converted to a floating electric power plant to supply the naval base at Guam, and Ponaganset, which broke in half and sank during her pre-reactivation overhaul. The Escambias were retired to the National Defense Reserve Fleet by the end of the 1950s, while the somewhat more economical Suamicos soldiered on through the Vietnam War; Cowanesque struck a reef and foundered off Okinawa in 1972. Because of their 7.5 megawatt generating capacity, six of the Escambias were transferred to the United States Army and converted to floating power plants in 1965–66, serving in that role in Vietnam. When Saugatuck went to the breakers in 2006 she was the last survivor of the Navy's Type T2 oilers.

Ships of the class

Name	Original name	Commissioned	USNS service	Fate
T2-SE-A1 (Sun Shipbuilding & Drydock, Chester, Pennsylvania)
USS Suamico (AO-49)	Harlem Heights	10 Aug 42	1948–1974	Struck 1974; scrapped 1975
USS Tallulah (AO-50)	Valley Forge	5 Sept 42	1949–1975	Struck 1986, scrapped 1987
USS Pecos (AO-65)	Oriskany	5 Oct 42	1950–1974	Struck 1974; scrapped 1975
USS Cache (AO-67)	Stillwater	3 Nov 42	1948–1973	Struck 1986, scrapped 1987
USS Millicoma (AO-73)	Kings Mountain	5 Mar 43	1949–1976	Struck and scrapped 1987
USS Saranac (AO-74)	Cowpens	22 Feb 43	-	To floating power plant 1946, reclassified YFP-9 1954. Struck 1956, sold 1957 (Somerset)
USS Saugatuck (AO-75)	Newtown	19 Feb 43	1948–1974	Struck and scrapped 2006
USS Schuylkill (AO-76)	Louisburg	9 Apr 43	1949–1976	Struck 1986, scrapped 1988
USS Cossatot (AO-77)	Fort Necessity	20 Apr 43	1949–1974	Struck 1974, scrapped 1975
USS Chepachet (AO-78)	Eutaw Springs	27 Apr 43	1949–1972	Struck 1980
USS Cowanesque (AO-79)	Fort Duquesne	1 May 43	1950–1972	Sank off Okinawa 1972
T2-SE-A2 (Bechtel Marinship, Sausalito, California)
USS Escambia (AO-80)		28 Oct 43	1950–1957	To Army as floating power plant 1966, scrapped 1971
USS Kennebago (AO-81)		4 Dec 43	1950–1959	To Army as floating power plant 1965, sold to RVN 1974
USS Cahaba (AO-82)	Lackawapen	14 Jan 44	1950–1958	To Army as floating power plant 1966, scrapped 1971
USS Mascoma (AO-83)		3 Feb 44	1950–1959	Struck and sold 1959 (Seatrain Oregon, Transchamplain), scrapped 1980
USS Ocklawaha (AO-84)		9 Mar 44	1949–1959	Struck 1959, scrapped 1975
USS Pamanset (AO-85)		30 Apr 44	1949–1957	Struck and sold 1957 (Seatrain Florida), to NDRF 1975, scrapped 1986
USS Ponaganset (AO-86)		15 May 44	-	Sank dockside at Boston 1947, wreck scrapped 1949
USS Sebec (AO-87)		29 Mar 44	1950–1957	To Army as floating power plant 1966, scrapped 1974
USS Tomahawk (AO-88)		16 Apr 44	1947–1960	Sold 1966 (Seatrain Maine), to NDRF 1973, scrapped 2008
USS Pasig (AO-91)	Mission San Xavier	28 Aug 44 as AW-3	-	Decommissioned 1955, struck 1960, scrapped 1975
USS Abatan (AO-92)	Mission San Lorenzo	29 Jan 45 as AW-4	-	Decommissioned 1947, struck 1970, SINKEX 1980
USS Soubarissen (AO-93)	Mission Santa Ana	5 Jan 45	1948–1958	Struck 1961, scrapped 1982
USS Anacostia (AO-94)	Mission Alamo	25 Feb 45	1948–1957	Struck 1957, sold 1967 (Penn Ranger, Omnium Ranger), scrapped 1978
USS Caney (AO-95)	Mission Los Angeles	25 Mar 45	1950–1959	To Army as floating power plant 1966, sold to RVN 1974
USS Tamalpais (AO-96)	Mission San Francisco	20 May 45	1948–1957	To Army as floating power plant 1966, sold to RVN 1974
T2-SE-A3 (Bechtel Marinship, Sausalito, California)
USS Cohocton (AO-101)		25 Aug 45	1949–1958	Sold 1967 (Transoneida), scrapped 1980
USS Concho (AO-102)			1948–1958	Completed as USNS Mission Santa Ana (T-AO-137) Oct 1945, struck 1958
USS Conecuh (AO-103)			1947–1957	Completed as USNS Mission Los Angeles (T-AO-117) Oct 1945, struck 1957
USS Contoocook (AO-104)			1947–1957	Completed as USNS Mission San Francisco (T-AO-123) Oct 1945, sank at New Castle DE 1957

Notes

^ The Liberty ship design avoided the problem by using reciprocating steam engines
^ Turbo-electric propulsion was not new; the battleship New Mexico had been built with it in 1915, as were five more battleships and two aircraft carriers

[1] The Liberty ship design avoided the problem by using reciprocating steam engines

[2] Turbo-electric propulsion was not new; the battleship New Mexico had been built with it in 1915, as were five more battleships and two aircraft carriers

[1]

[2]