It took the pressure of the Second World War in the Pacific, which reached into the far corners of that ocean, to make Underway Replenishment (UNREP) a regular feature of Naval Operations. The war in the Pacific made new demands on the Navy -- supply lines had to be extended, quickly, in order to project power across the oceans and keep it there.
Underway Replenishment is the method by which provisions, ammunition and fuel are transferred from one ship to another at sea. The technique of replenishment at sea enables a fleet or naval formation to remain at sea for prolonged periods of time. There are two methods by which UNREP is accomplished:
The Navy operates a Combat Logistics Force fleet of about 40 ships that resupply combatant ships at sea with several commodities. The ships carry significant amounts of these commodities, for example, ship and aviation fuel (DFM and JP-5, respectively), ordnance, and other supplies such as ship and aircraft fuel, ordnance, and food, which enables combatant ships to operate at sea almost indefinitely, if required, without ever needing to go into ports to replenish their stocks. The force represents additional days of sustainability for the naval force by serving as an extension of the combatant ships' bunkers, magazine and store rooms.
Capacities of Selected Combat Logistics
Force Ships
Other
Class Speed Fuel\ a Ordnance supplies
---------------------- ---------- ---------- ---------- ----------
(knots) (barrels) (tons) (tons)
(T-) AE-26 20 \b 6,000 \b
(T-) AFS-1 20 18,000 \c 7,000
AO-177 20 150,000 625 420
(T-) AO-187 20 180,000 \c \d
AOE-1 30 177,000 2,500 750
AOE-6 30 156,000 1,800 650
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Note: T-class Combat Logistics Force ships are operated by the
Navy's Military Sealift Command. These ships use civilian, instead
of military, crews but may have a small military detachment aboard.
A majority of the non-AOE class ships are now operated by the
Military Sealift Command.
\a Reflects a combined total for DFM and JP-5.
\b Primary mission is ordnance replenishment. Limited quantities of
fuel and other supplies are also available.
\c No ordnance carried.
\d Primary mission is fuel replenishment. Limited capacity to carry
other supplies.
Average Daily Fuel and Ordnance
Consumption Rates for Selected Ship
Classes
DFM JP-5 Ordnance
Ship class (barrels) (barrels) (tons)
---------------------------- ------------ ------------ ------------
Carrier (CV) 2,700 6,500 70-150
Carrier (CVN) \a 6,500 70-150
CG-47 725 \a \a
DD-963 710 \a \a
DDG-51 710 \a \a
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\a No quantities shown.
Evaluated force levels for various scenarios show that station ships are required to maintain battle group
endurance. The ability of the AOE's to provide all replenishment services simultaneously minimizes the
non-operational time of the battle group. Alternatives which use multiple shuttle ships in combination to
perform the station ship functions (such as AORs combined with AEs) require multiple replenishment
which, coupled with their slower speed, reduces the on-station time of the battle group. These
combinations are more expensive to operate and exacerbate the shortfall of AE ships.
The conventionally powered cruisers and destroyers that are a part of carrier battle groups are dependent on underway replenishment support by Combat Logistics Force. Compared to a conventional carrier, they have smaller fuel storage capacities and relatively high fuel consumption rates at higher speeds. Station ships travel with carrier battle groups. They carry petroleum products, ordnance, and other supplies and are generally replenished by shuttle ships operating from land-based facilities worldwide. The presence of a station ship in the battle group extends the group's range considerably.
There are several UNREP areas that are candidates for improvement. Selected areas for improvement, consideration and industry involvement are listed below: