Replenishment oiler

A replenishment oiler at work

A replenishment oiler is a naval auxiliary ship with fuel tanks and dry stores capability, which can replenish other ships underway. The US Navy hull classification symbol for this type of ship is AOR. Classes include the Wichita class ships of the US Navy, the Soviet/Russian Boris Chilikin type, and the Canadian Protecteur class. They are slower and carry fewer dry stores than Fast Combat Support Ship (AOE) ships. The Wichita class of AORs will be discussed in detail in this article, and links to other classes of AORs will be given at the end of the article.

OVERVIEW

The US Navy Wichita class of AORs comprises seven ships, listed at the end of this article. The class ship was commissioned in 1966, and the last ship, the USS Roanoke, was commissioned in 1976. The naming convention for these ships was that they be named for smaller US cities which have rivers of the same name. All ships of this class have been retired from service, and are being held by [[MARAD}} in the inactive ("mothball") fleet (National Defense Reserve Fleet, a.k.a. NDRF).

HISTORY OF DESIGN

The forerunner of this design was a Kriegsmarine (German Navy) ship, the Dithmarschen, which was built in 1938. The Dithmarschen was designed to provide fuel and stores (including munitions) in a "One Stop Shopping At Sea" context to the German fleet. After the war she was claimed by the United States as a war prize and commissioned into the United States Navy as the USS Cohecuh (AOR-110). She proved the feasibility of this sort of vessel in supporting task forces at sea. She was decommissioned in 1956. The Wichita class was one variant on this concept later developed by the U.S. Navy, the other variant being the larger and faster AOE class of fleet replenishment oiler.

CHARACTERISTICS OF US AOR DESIGN

The modern US AOR-1 class of ships was designed primarily to support anti-submarine task forces. These ships gross just under 40,000 tons, have a length of 651 feet (198 m), a beam of 96 feet (29 m), and a draft of about 35 feet (10.7 m) fully loaded. They are equipped with highly automated fuel and cargo handling systems, and are capable of underway replenishment (UNREP in Navy terminology) from both port and starboard sides simultaneously, and also can transfer stores and munitions by helicopter (vertical replenishment or VERTREP). The ship's complement is 34 officers and 463 enlisted.

ARMAMENT

These vessels are suppport vessels, not combat units. As delivered by the shipyards they were equipped with two 5"/38 guns (five inch, 38 calibre), located aft on the 02 level. This is illustrated by the photo of the USS Wabash (AOR-5) shown above. However, as each ship was drydocked for maintenance, the guns were removed and replaced with a helo hanger, and the ships were equipped with two CH-46 Sea Knight helicopters, two Phalanx close-in weapons systems (CIWS) and one Mk-29 Sea Sparrow point defence system.

SHIP LAYOUT

These vessels have two superstructures. The forward superstructure houses the bridge, a Combat Information Center (CIC), the Captain's quarters, various support facilities, and the pilot house. The after superstructure houses the crew's quarters, various support facilities, the helo deck, and a centerline elevator extending from the main deck to the 02 level for use in material (VERTREP) transfer.

These ships are unusual for naval vessels in that the fire room is aft of the engine room, and the shafts extend through the fire room and the steering engine room. From aft forward, the engineering spaces consist of the steering engine room, the fire room, and the engine room. The forward bulkhead of the engine room abuts onto cargo tanks. All boilers are in the single fire room, and both engines are in the single engine room. There are two hydraulic steering engines in the steering engine room, controlled either locally by a trick wheel or by the helmsman in the pilot house. They are powered by three Foster-Wheeler D-type steam generators operating at 600 PSI, driving two engines with a combined power output of 33,000 SHP (shaft horsepower), giving them a maximum sustained speed of about 22 knots. They are equipped with twin rudders. The plant auxiliary machinery is all electric, and they are equipped with four 2,000 KW electric generators. There are two deck elevators on the main deck, and they can accomodate a large amount of dry cargo, including refrigerated and frozen stores, on the second deck. They have two pump rooms for fuel transfer, and commonly transfer Navy Distillate (ND), Number 2 diesel fuel, and JP-5 They also carry and transfer aviation gasoline, for which a separate pump room, set of tanks, and transfer facility is located on the forecastle (foc'sul). The US Navy will as a matter of policy neither confirm nor deny that these ships are equipped for the storage and transfer of nuclear weapons.

REASON FOR RETIREMENT OF CLASS

There are several reasons for the retirement of the AOR class. First, they are designed primarily for support of anti-submarine (ASW) task forces. In this the principal enemy was the Soviet Union, which has ceased to pose a submarine threat to the United States. Second, being smaller and slower than the US AOE class of replenishment ships, they are not suitable for support of fast aircraft carrier task forces. These ships are also steam ships, which are more expensive to operate than more modern gas-turbine powered ships. Finally, all ships of this class are single-hull ships, as opposed to modern double-hull ships. As such, continued operation is seen to pose an unacceptable risk to the environment in the case of collision or other hull breach.

SHIPS IN CLASS

• USS Wichita, AOR-1
• USS Milwaukee, AOR-2
• USS Kansas City, AOR-3
• USS Savannah, AOR-4
• USS Wabash, AOR-5
• USS Kalamazoo, AOR-6
• USS Roanoke, AOR-7

AOR CLASS SHIPS IN OTHER NAVIES

Navies other than the U.S. Navy are actively designing and building fleet replenishment oilers of the AOR class. These navies, including the Royal Australian Navy and the Spanish Navy, have requirements that do not include high speed and high capacity; thus an AOR design meets the logistics needs of these navies better than would a larger, faster AOE design.

REFERENCES AND EXTERNAL LINKS

• [1] DANFS USS KALAMAZOO (AOR-6) website
• [2] US Naval Vessel Register
• [3] KMS Dithmarschen
• [4] Spanish Navy Patino Class AOR
• [5] HMAS Success, AOR-304