Underway Replenishment
AUTHOR LtCdr. Donald D. Hill, USN
CSC 1989
SUBJECT AREA - Logistics
EXECUTIVE SUMMARY
UNDERWAY REPLENISHMENT
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
support.
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
future.
UNDERWAY REPLENISHMENT
OUTLINE
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
1. STREAM
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
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
I.
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.
(13:77)
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.
(5:50-51)
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)
TABLE 1
URG TRANSIT TIMES
OPERATING RESUPPLY DISTANCE (NM) ROUND TRIP
AREA POINT TIME (DAYS)*
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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