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Underway Replenishment

Underway Replenishment


AUTHOR LtCdr. Donald D. Hill, USN


CSC 1989


SUBJECT AREA - Logistics








Underway replenishment has always been recognized as

important, but took a back seat in development until it was

absolutely required. Research indicates that underway

replenishment dates back to the days of sail. Since then,

there have been four major periods in the development of

underway replenishment. The first was at the turn of the

century when coaling-at-sea was investigated. The second

was refueling-at-sea development. The third was underway

replenishment during World War II and the Korean War. The

final period was the late l95Os when the modern underway

replenishment concept was developed.

From the underway replenishment concept came the modern

underway replenishment ships and equipment. Underway

replenishment by these ships has evolved into a highly

efficient and reliable system that can replenish the naval

fleet day or night in all kinds of weather. This

replenishment is accomplished using single-product

replenishment ships (fleet oilers, combat stores ships, and

ammunition ships) and multi-product ships (fast combat

support ships and replenishment oilers). Each ship's

capabilities are taken into account when deciding what type

of ship is going to be used to handle fleet commitments.

There are not enough replenishment ships to handle all

the replenishment requirements that could occur during a

major crisis when much of the fleet would need support.

The Navy is looking at using various merchant tankers and

containerships to aid the Navy replenishment ships in fleet


Underway replenishment has positive direction and

enjoys higher status than the past. New ships are being

built, new equipment is being developed, and new ship types

are being explored to carry underway replenishment into the








Thesis Statement: The US Navy underway replenishment


program has come through the time of forced development to


an evolving doctrine that will adequately serve the fleet.


I. History of Underway Replenishment


A. Days of Sail


B. Coaling at Sea


C. Eearly Refueling/World War I


1. USS Maumee


2. Close-in fuel rig


D. World War II


E. Korean War


II. Modern Underway Replenishment Concept


A. Designed-For-Purpose UNREP Ships


B. Multi-Product UNREP Ships


III1. Cargo Transfer System


A. Connected Replenishment




2. Rig configuration


B. Vertical Replenishment


IV. Fleet Replenishment


A. Battle Group Replenishment


B. Underway Replenishment Frequency


C. Underway Replenishment Ship Shuttle


D. Ship Requirements



E. Mini-Multi Concept


F. Merchant Augmentation


V. Future of Underway Replenishment


A. New Ships


B. New Equipment







Underway replenishment for the US Navy has become a


routine, common occurrence for ships at sea. Everything


needed at sea can be transferred while underway; fuel,


food, ammunition, parts, personnel, and mail are


transferred. This reliable, fast transfer-at-sea has not


always been a navy luxury.


Underway replenishment has been required by the US


Navy since its earliest days. Underway replenishment has


been piecemeal, improvised, and lacking direction until


recent times. There is hope on the horizon, and the hard


lessons of the past have been learned. The US Navy


underway replenishment program has come through the time of


forced development to an evolving doctrine, that will


adequately serve the fleet.


The US Navy conduct of underway replenishment dates


back to the earliest years of the Navy. During the


Quasi-War with France (1799-1801) the young United States


traded only in the Caribbean. The neutral US shipping was


harassed by French warships and various privateers. The


Navy was sent to the area to defend US interests. (lO:159)


One particular ship squadron whose flag was USS



Constitution was assigned duty off Haiti. The slow down of


local privateering due to the presence of the US ships had


made the US warships not welcome in Haitian ports. These


were the closest ports for replenishment. The USS


Constitution and squadron had to stay on station to carry


out their mission and could not go off station as would be


required by going to other friendly ports to replenish food


and other items. The Navy Department chartered various


merchant vessels to rendezvous with the USS Constitution


squadron for resupply. The merchant would rendezvous with


a warship and be taken under tow. The stores would be


transferred by ship's boats. This setup allowed the


warships to stay on station. (10:161)


The US Navy also used the frigate USS John Adams with


reduced armament to shuttle men and supplies from the


Chesapeake to the Mediterranean during the war with


Tripoli. (6:78)


Sailing ship UNREPs pale in comparison to UNREP


requirements that were coming with the modern, mechanized


fleet. The first and foremost problem was one of fuel.


The early steam powered ships required large amounts of


coal to operate. The problem of ship coal replenishment


first arose during the Civil War. No method of coaling on


the open sea existed. At any one time, one-quarter of


Union ships on blockade duty were required to be off


station in a nearby friendly port filling their coal



bunkers. (16:157) While very inefficient, no alternatives


were offered


During the Spanish-American War large numbers of US


Navy steam-powered ships were required to fight outside the


continental shores. (12:2) To refuel these ships, merchant


colliers were procured. Coaling was done underway by


bringing the collier alongside the customer ship, placing


fenders in between, and lashing the ships together with


mooring line. Booms on the collier would transfer


the coal to the customer. (15:8) If the sea state became


too rough, the replenishment would have to stop until the


weather calmed, or the ships would have to move to a


sheltered anchorage and transfer the coal at anchor. While


on blockade duty off Santiago de Cuba, the weather was so


rough most of the time that ships had to go to Guantanamo


Bay to recoal. Again one-quarter of the fleet was off


station at any one time taking on coal. USA Massachusetts


and two other ships were 45 miles away recoaling in


Guantanamo Bay and completely useless when the Spanish


fleet came but of Santiago. (16:159-160)


The problems with coaling during the Spanish-American


War led to engineering research in coaling-at-sea mainly by


the engineer, Spencer Miller, Esq. He developed an under-


way coaling-at-sea system in 1904, but when tested, it


operated poorly. The next decade was spent redesigning and


refining this system. The revised system showed promise,



but the development was stopped. Coaling-at-sea had re-


ceived a bad name among naval officers from the 1904 expe-


rience, and with the emergence of fuel oil for navy


boilers, coaling-at-sea became a less critical


requirement. (13:76)


With the emergence of fuel oil as the fuel of choice,


the Navy built a diesel powered oiler the USS Maumee (AO 2)


in 1916. The oiler was designed to transfer fuel oil to


warships while at anchor. Small ships came alongside the


oiler, but the oiler went alongside the battleships. (18:10)


The USS Maumee's crew discussed and developed a plan


to refuel ships while underway, but had no opportunity to


test the plan. At the outbreak of World War I, USS Maumee


was sent to the mid-Atlantic 300 miles south of Greenland.


This location was a rendezvous position to refuel US


destroyers enroute to England who could not transit across


the Atlantic unless they refueled. The destroyers would


approach USS Maumee who would pass a 10-inch manila hawser


which was then secured to the destroyer. The destroyer


would slow to maintain good steering control-and a spacing


of about 50 feet would result. A four-inch fueling hose


was then passed to the destroyer and supported by a wooden


saddle suspended from cargo booms on the USS Maumee. The


hose was lead directly to the-destroyer's fueling bunker,


and fuel was pumped by USS Maumee. In addition to fuel,


stores and personnel could be transferred using the cargo



booms. The whole UNREP took about two hours per


destroyer. USS Maumee refueled 34 destroyers enroute to


Europe while on station approximately three months in


1917. (18:10-11)


This same system was used for Navy fuel UNREPs through


World War II. As ship rudder controls were made more


sensitive and reliable the 10-inch hawser was deleted, but


the rest of the procedure was unchanged. (18:12) (It is still


used today and is called the close-in fuel rig.) After


World War I refueling underway at sea was looked upon as an


emergency operation that may have to be resorted to in


wartime. It was a tolerated, annual exercise. (4:3)


World War II produced the great task of supporting the


fleet from the US west coast and Hawaii far out to the


operating areas in the Pacific. Floating logistic support


was the only alternative to this tremendous undertaking.


However, the depression had left the Navy lacking for


support craft of any kind, so they had to be made and


pressed into use after the war started.


Most Pacific World War II naval shipping was supplied


at anchor by small supply craft designed or built for


specific functions. As the fleet fought toward, Japan, the


logistic support also moved to forward bases on nearby


friendly islands or atolls. Merchant ships brought


supplies to the forward bases. Here they would deliver to


the small craft for resupplying ships at anchor, or they



would resupply the oilers of the Fast Attack Carrier


Forces. These oilers were the only ships to conduct actual


UNREPs during World War II, and then they conducted UNREPs


only with the aircraft carriers and escorts. They used the


method developed by USS Maumee. As the war progressed,


shipping increased to support the war, but at the end of


World War II, the majority of the large logistics Navy was


deactivated. It was theorized that all Pacific


requirements could be handled from Hawaii or CONUS. (6:78)


When the Korean War broke out in 1950, the US had very


few logistics ships to support the war. The ships


available were sent to Korea from all over the Pacific.


Ships from World War II were reactivated and loaded as


quickly as possible. The same jury rigged replenishment


methods used during World War II had to be employed.


While these methods may have worked-in World War II, they


were not sufficient to handle the tempo of operations off


Korea. Using merchant ships to rearm aircraft carriers was


found to be inefficient and unsafe. (13:76) Some slight


improvements were made as the war progressed, but new


problems appeared. (12:4-5)


The magnitude of problems that occurred during the


Korean War led the Chief of Naval Operations to call a


conference at San Francisco Naval Shipyard in 1952 which


put engineering back into UNREP for the first time since


1913. (12:5) One result of this meeting was a shipbuilding



program that produced the first "designed-for-purpose"


(12:5) UNREP ships. An oiler, a stores ship, and an


ammunition ship came out of this program. There existed a


major drawback with these new ships. The ships were larger


and faster than their World War II counterparts, but no


improvement had been made in the underway transfer


capability. (12:5) The UNREP method was still pre-World War




A new UNREP concept started to emerge. In 1957, a


conference convened by the Chief of Naval Operations,


Admiral Arleigh Burke, "called for a new underway


replenishment system that minimized the time for UNREP and


could be conducted day or night in fair weather or foul."


(12:7) Out of this direction came the concept of a


multi-product UNREP ship. This concept allowed combatant


ships to go alongside one UNREP ship and get everything


needed in only one stop instead of having to go alongside


three single-product ships. Aircraft carrier replenishment


time was reduced from ten hours to three. (13:76)


The first ship designed was a fast combat support ship


(AOE). The AOE was sized to have the fuel capacity of a


fleet oiler, the ammunition capacity of an ammunition ship,


and a partial dry cargo capacity of a stores ship. The


hull design was configured using a battleship because of


its excellent course and station keeping capabilities. The


AOE was given the speed to stay with and be protected by



the aircraft carrier battle group (CVBG). This also allows


combatants to UNREP anytime enemy and operational


commitments permit. (13:76)


An AOE would be nothing more than a fast, expensive


cargo ship were it not for the "high-performance, all-


weather cargo transfer system. "(13:77) The transfer rig is


a modern version of what was tested and developed by


Spencer Miller, Esq. at the turn of the century.


Transferring either coal bags or ammunition pallets has


been found to be very similar. The rig is called the


standard tensioned replenishment alongside method


(STREAM). It uses a hydraulic ram tensioner to keep a wire


highline tensioned between the UNREP ship and the


combatant/customer ship. A one-inch wire rope is passed to


the customer by the UNREP ship. It is attached to a


special attachment point on the customer ship. The slack


is removed, and the ram tensioner keeps up to a 300-foot


highline (maximum ship separation) taut no matter how the


ships roll. A trolley rides this highline and transfers


loads between ships. The largest, heaviest missiles and


aircraft engines are lifted by a sliding block on the UNREP


ship, transferred to the customer by the trolley, and


lowered to the customer's deck by a sliding padeye.


Transfers of two-minutes-per-load are normally achieved.




UNREP ships are configured with priority of transfer



to aircraft carriers. Aircraft carriers can only UNREP to


their starboard sides, so UNREP ships have the highest


number of STREAM rigs to their port side. Most UNREP ships


are built with four port side delivery stations and three


starboard side delivery stations. This configuration


allows simultaneous aircraft carrier UNREPs to the port


side of the UNREP ship and escort ship UNREPs to the


starboard side.


In addition to the STREAM stations, sixty percent of


current UNREP ships have helicopter hangars and can carry


two H-46 helicopters for vertical replenishment (YERTREP).


The H-46 helicopter can carry loads internally as well as


externally. For VERTREP the load is normally a 4000 pound


external load. The helicopter hovers over the UNREP ship,


a load is attached to the helicopter via a hook and


pendant, the load is picked off the deck of the UNREP ship


and taken to the customer ship, the helicopter hovers over


the other deck, and the load is released and set on the


deck of the customer ship. With two ships nearby, VERTREP


can handle about the same amount of stores or ammunition as


a STREAM rig. Neither fleet oilers nor the five older


ammunition ships carry helicopters. The 17 oilers don't


carry enough dry cargo, and the five ammunition ships do


not have space for a hangar.(12:11-12)


CVBG replenishments are done with one AOE or one re-


plenishment oiler (AOR). An underway replenishment group



(URG) consisting of one oiler (AO), one ammunition ship


(AE), and one combat stores ship (AFS) in turn support the


AOE/AOR. The URG shuttles to and from the nearest supply


base. Upon arrival in the operating area the URG would


either replenish the CVBG directly, or they would


consolidate (transfer from one UNREP ship to another) their


loads with the AOE/AOR which would then replenish the


CVBG. The URG would then return to the supply base and


repeat the shuttle processa


The CVBG endurance is a function of UNREP frequency.


The length of time between UNREPs is based on fuel,


ammunition, and food consumption. Food consumption is


constant. Fuel and ammunition consumption rates vary.


ammunition and fuel consumption is based on the type of


operations being conducted, and their usage will increase


significantly as the tempo of operations increases. (5:50)


This could require more frequent UNREPs.


Based on computed consumption rates a CVBG should


UNREP every four days. Examining a CVBG operating in the


Indian Ocean and taking into account URG transit times


shows that at least two URGs would be required to resupply


from Diego Garcia. One URG UNREPs the CVBG and commences


the return trip to Diego Garcia while the other URG


resupplies in Diego Garcia and begins its transit back to


the CVBG. If Diego Garcia is not available, and the URG


has to transit to Subic Bay, RP, or Perth, Australia, at



least five URGs would be required to sustain the CVBG.




Table 1 lists distances and transit times required for


URG transits to various parts of the world. The table


assumes an 18 knot transit speed and does not include ship


loadout time. (5:50)








Eastern Med Naples, Italy 500 3

Rota, Spain 1300 6


North Portsmuth, UK 900 4

Atlantic Azores 1500 7

United States 3900 18


North Yokosuka, Japan 1400 7.5

Pacific Subic Bay, RP 3000 14

United States 4000 18.5


Indian Ocean Diego Garcia 1700 8

(Arabian Sea) Mombasa, Kenya 1700 8

Perth, Australia 4000 18.5

Subic Bay, RP 4000 18.5



The Navy currently has 11 AOE/AORs to support the 15


CVBGs. There are 13 AEs, 18 AOs, and 7 AFSs. These


numbers show that the minimum requirement of one AOE/AOR


and one URG per CVBG can not be attained, let alone


supported. At a minimum, two to five URGs (6 to 15 ships)


would be required just in the Indian Ocean. Given the


overall strategy of CVBGs operating simultaneously


throughout the world, a worst case requirement calls for as



many as 25 URGs (75 ships) being required to sustain


operations. This is considerably higher than the current


7-12 URGs (21-36 ships.)


In an attempt to alleviate the UNREP ship shortfall,


single-product ships (AO, AE, AFS) have been modified to


mini-multi-product delivery. On the AE and AFS, one


starboard side transfer station has been configured for


refueling of destroyers and frigates by transferring own


ship cargo fuel. The fuel pumping rate is slow but


workable. The AO and AE can be outfitted with three


20-foot refrigerated deck cargo containers to carry


provisions. These modifications allow a single-product


ship to service the fleet when a multi-product ship is


unavailable. (12:12-13)


Another way to relieve the UNREP ship shortfall is to


use commercial tankers and containerships to augment US


Navy shipping. However, commercial ships-can only be used


to resupply UNREP ships and not combatants. One idea is to


modify merchant tankers at one of two possible levels. The


lower level of modification would add two port and one


astern refueling stations, two port and two starboard UNREP


attachment points, a limited US Navy communications


package, and two electrical generators to support the added


equipment. The higher level of modification would add to a


tanker three port and two starboard refueling stations, an


OMEGA Navigation system, an extra gyrocompass, a full US



Navy communications package, and significant safety


enhancement equipment. To either modified tanker could be


added a helicopter deck area, a sliding padeye for dry


cargo transfer, and a raised Mecanno deck. (19:35-36) The


Mecanno deck is an erector set style raised platform to


carry outsize cargo or modern cargo containers. (14:224)


Containerships can transfer supplies from point-to-


point as designed. Problems arise because the US Navy


requires breakbulk ships not containerships. Also if the


containership destination is not equipped to handle the


containers, the ship can not be offloaded. Ordnance


transfer is also a problem as easy access is required to


the cargo. (19:38) Two systems are available to modify


containerships to help solve these problems as all new


cargo ships being built are containerships. One is a


modular elevator in which the elevator shaft and equipment


are built into standard cargo containers. The other system


is a flat rack. The flat rack is a container without a top


and sides. The flat rack-can be used as a cargo bridge and


allow access to loaded containers. Using the modular


elevator and flat racks roughly turns a containership into


a breakbulk ship. The extent of these modifications, hence


US Navy usage, is limited as the number of US merchant


ships is declining.


The future of UNREP is bright. The US Navy is


building new Military Sealift Command oilers to UNREP the



fleet. These oilers are the same as the improved USS


Cimarron (AO 177) class oiler and will replace aging World


War II era oilers. Another development is a new gas


turbine powered AOE, the AOE 6 class. The keel for AOE 6


has been laid, and up to fifteen ships of this class may be


built. This will enable the replacement of older


ammunition ships and ensure at least one multi-product ship


for each CVBG. The trend in the US Navy is to continue to


build multi-product vice single-product UNREP ships. The


latest proposal is to build a ship with the capabilities of


both an AE and an AFS.


The US Navy is also continuing to develop new UNREP


equipment to be used on the new ships. A new refueling


hose is under development. The hose is made of


polypropylene and is light weight and durable. With this


new hose it may be possible to conduct refueling without a


wire highline. Only the hose will have to be passed by the


UNREP ship. Another new idea is that of tensioned


connect-up. Instead of all the line that has to be handled


to connect two ships during an UNREP, a small stainless


steel wire rope will be passed to the customer and the


highline and associated equipment will be pulled over by


the UNREP ship using this small wire. A program to


standardize all UNREP equipment for the NATO navies is also


in progress.


The US Navy UNREP program has come a long way from the



days of sail to the present day. The UNREP concept


developed 30+ years ago is still as viable today as it was


when developed. It continues to shape the UNREP program


and will do so into the next century. The value and


importance of UNREP is fully realized, and is getting the


attention it deserves.





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