Underway replenishment (UnRep), the Navy’s “secret weapon of World War II” as coined by Fleet Admiral Chester Nimitz, has enabled historically unprecedented, sustained combat operations by the U.S. Navy. Continuing that tradition in the age of distributed lethality requires hard decisions and focused prioritization of UnRep system development and installation.
In 1916 and 1917, while serving as chief engineer and executive officer of USS Maumee (AO-2), Lieutenant Nimitz, his commanding officer, Lieutenant Commander Henry C. Dinger, and their ingenious crew created—nearly from scratch—a procedure to refuel ships while under way and making way. This was a significant departure from the then-current methods of mating alongside in protected harbors or the previous experiments in astern refueling. The Maumee deployed that capability operationally for the first time on 28 May 1917, replenishing six destroyers en route from New York to Ireland, and would go on to refuel 34 other ships in the next months. A decade later, the process was expanded to enable refueling destroyers and escort ships from battleships and aircraft carriers (an evolution still practiced today). It was not until 1939 that refueling capital ships was attempted, and several more years before it became common practice.
A significant leap forward came when Admiral Raymond A. Spruance directed the further expansion of replenishment to include ammunition. The idea was to keep his Task Forces’ (TF) aircraft carriers and ships from having to return to a forward operating base 2,000 nautical miles away, avoiding a 10- to 12-day replenishment cycle in favor of a one-day, two-night turnaround. It was at this point that UnRep first enabled an entire fleet to remain under way for months, able to strike at the enemy with few constraints, and Spruance’s forces did just that. TF 38 and TF 58 operated nearly independent of forward-operating bases from February 1944 through September 1944 while conducting strikes in support of the Okinawa and Iwo Jima campaigns. They expended more than 15,000 tons of ordnance and consumed more fuel in three months than Japan imported or produced in all of 1944.
The UnRep process, however, remained cumbersome and inefficient. TF 38 lined up along a 40-nautical-mile front prior to dawn and every ship would execute three complete UnReps: one for fuel, one for ammunition, and one for stores. It was during these long and taxing days that then-Captain Arleigh Burke recognized the value of the time consumed during UnReps, saying, “All time spent in replenishing was time lost in combat. This is when I had impressed on me the value of time. No fleet commander can ever tell what a few minutes might mean in the future.”;
While serving as the Chief of Naval Operations in 1957, Burke supported a ship design proposal that would become what is now known as fast combat stores ships (AOEs), which are capable of delivering fuel, ammunition, and stores in a single evolution. Adding to this capability was the development of the standard tensioned replenishment alongside method (STREAM) system at the then newly formed Naval Ship Missile Systems Engineering Station (NSMSES), now the Naval Surface Warfare Center, Port Hueneme Division (NSWC PHD). The establishment of the Military Sealift Command and placing civilian mariners on board logistics ships—beginning with the USS Taluga (T-AO-62) in 1972—also played a significant role in establishing the UnRep capabilities and procedures used today.
As capable as it is at UnRep, the Navy has not invested in new capabilities to keep pace with future warfighting requirements. The value of time that Admiral Burke understood so well has eroded. While the Navy has worked to make surface ships and naval air forces more lethal at longer ranges, it has allowed its abilities to sustain combat operations at sea to deteriorate. Without new investment, soon the fleet may be required to do what the Navy worked so hard to avoid in World War II: return to forward-operating bases to replenish. The Navy needs better systems to load ammunition—including vertical launch system (VLS) ordnance handling systems—and more replenishment ships.
An aircraft carrier’s primary capability is defined by its sortie rate (the number of mission-capable aircraft launched to assigned tasking), but the current STREAM systems on board AOEs were designed to keep Kitty Hawk (CV-63)-class carriers continuously armed to support their sortie rate (in weight of ammunition and the speed of transfer: 5,700 pounds per load at 12 loads per hour). This capacity was stretched to meet the needs of the Nimitz (CVN-68)-class carriers. The Ford (CVN-78)-class aircraft carriers, with their advanced systems, are designed to generate significantly more sorties than the Nimitz class—making the current STREAM system inadequate to the task of supplying the ammunition and fuel required to support full sortie generation rates. Simply put, a significant increase in sorties will require a proportional increase in UnRep time to keep those aircraft flying and armed—more sorties will mean more alongside time. This creates a limiting factor to the sortie rate because of time required off station. What is the value of that time?
In a contested maritime environment, a capital ship’s time in a forward-operating area is limited to the time its escorts can protect it from missile threats, which is limited by the number of air defense missiles in the escort’s magazine. The group will have to leave station and transit to a VLS reload facility, reload the escort ships, and transit back to the operating area. Every combatant operating independently faces this challenge as well. Several attempts have been made to overcome this obstacle. In the 1960s an aborted system by the then-Surface Missile Systems Program sparked the creation of the UnRep division at NSMSES. Other attempts include an impressive six-degree of freedom crane developed by the Naval Research Office, which has demonstrated some success during in port and sea-state limited testing. Still another system, designed at NSWC PHD that could replenish 12 VLS canisters per hour, required the use of the retractable kingpost and so is no longer feasible. In limited wars over the past few decades, reloading VLS at sea has not been a requirement. In preparing for a possible war against a near-peer competitor, the Navy must develop a solution to this problem.
Finally, as the Navy moves forward with distributed lethality—demonstrated recently by the Pacific surface action group consisting of the USS Decatur (DDG-73), USS Momsen (DDG-92), and USS Spruance (DDG-111)—it has become clear that distributed lethality requires distributed UnRep capability. With ships spread across the theater of operations, replenishment ships will need to spend more time transiting to rendezvous sites, meaning that the value of time Admiral Burke spoke of applies equally to UnRep ships as it does to combatants—every moment spent alongside a combatant is a moment not spent transiting to the next one. The Navy has two choices: increase the number of replenishment ships, or decrease the time alongside. Increasing the number of replenishment ships might be as easy as re-emphasizing the use of capital ships to replenish smaller ships. Decreasing time alongside is more challenging.
Fortunately, the first new family of UnRep systems in more than 40 years—consisting of electric-STREAM, electric fueling at sea (E-FAS), and heavy E-STREAM—have been designed and built for some of these tasks. These new systems have proven reliable, compact, easy to use and maintain, and less damaging to cargo while maintaining complete compatibility with STREAM receiving stations, and their precision controls may be able to support a future VLS reload capability. In addition, two prototype heavy UnRep delivery stations have been built; one is installed at the UnRep test site in Port Hueneme and the second on board USNS Arctic (T-AOE-8) in 2012. A third will soon be installed in USNS Cesar Chavez (T-AKE-14). Designed to match the increased sortie generation rates, heavy E-STREAM increases the throughput from 12 5,700-pound loads per hour to 25 12,000-pound or 50 6,000-pound loads per hour between two heavy systems. If one ship does not have the heavy E-STREAM, the higher speed is still available but only at the original STREAM weights. The heavy E-STREAM system is part of the USS Gerald R. Ford (CVN-78) design, but has been removed from the John Lewis (T-AO-205)-class and the John F. Kennedy (CVN-79), and is not planned for back-fit to other replenishment ship classes. These decisions should be reconsidered lest sortie generation rates be limited by lack of ammunition.
Replenishment limitations not only affect aircraft carriers, destroyers, and cruisers, but also amphibious ships. Moving heavy Marine combat equipment from the sea base to an amphibious assault ship will exceed the capability of current STREAM systems, just as the weight of an F-35 engine does. Other methods exist for these transfers, but the flexibility of E-STREAM and heavy E-STREAM would add options.
E-STREAM systems build on the legacy of Navy UnRep technologies and procedures. They are the future of UnRep—if the Navy truly values time. The lessons of World War II remain germane, and at-sea replenishment always will be key to keeping combatants on station—especially in a high-end fight. To fight a near-peer competitor in the distributed manner envisioned, the Navy needs the entire E-STREAM family of systems on board its replenishment ships, aircraft carriers, and combatants, and must prioritize their installation in its budgets and shipbuilding plans.