Auxiliaries Part 2

Last time, we talked about how, in the years leading up to World War I, the US Navy developed an array of auxiliary ships designed to support the fleet in the absence of permanent bases. Most prominent among these were the oilers, some of which were used to refuel ships at sea. During the 1920s, as the plans for the war against Japan developed, it became increasingly obvious that the USN would need the ability to reliably refuel ships at sea to carry it off. While the latest destroyers were longer-ranged than the ships Maumee had refueled in the mid-Atlantic, their range was still insufficient for the broad Pacific. As a result, the alongside method of refueling was developed and perfected, to the point that it had become almost routine for the smaller craft. In addition to the oilers, battleships and carriers were also equipped to refuel their escorts.

Sabine refueling Enterprise during the Doolittle Raid

But the destroyers were not the only ships with worryingly short legs. The pre-turboelectric battleships had inefficient engines, and a method of refueling them at sea was desired. However, the alongside method was considered far too dangerous for use with any ship larger than a destroyer. Instead, trials were made of refueling over the stern. This removed the threat of small helm errors causing disaster, but turned out to have intractable problems of its own. The fueled ship had to be far astern, which limited flow rate and required inordinate pumping power.¹ Special equipment was required to keep the lines supporting the hose under tension. If the hose sagged into the sea, the oil would cool and thicken, interrupting the refueling.² Ultimately, the problem was solved by refitting the battleships in question with more efficient geared powerplants, and the matter of refueling big ships rested for the next decade.

Arizona refueling astern from the oiler Kanawha

In the late 30s, carrier operations made it increasingly apparent that the inability to refuel bigger ships at sea would be a serious hindrance in case of war. During the Fleet Problems, carriers routinely burned as much as 10% of their oil each day. Finally, in the spring of 1939, trials were made with larger vessels using the alongside method under the command of now-Rear Admiral Nimitz.³ They were successful, and the fleet’s few oilers were soon being used extensively for development work.

Cimarron off Norfolk, 1942

In the late 30s, for the first time since WWI, the Navy began to buy oilers. They sought ships capable of keeping up with the fleet at cruising speed, which meant a speed of 16.5 kts, as opposed to the 13 kts typical of tankers at the time. The resulting T3 tanker was designed by the Maritime Commission and the first batch was laid down for various oil companies. Three of the first twelve were taken over before delivery as the first units of the Cimarron class, which eventually numbered 35 ships.⁴ Turning a civilian tanker into a fleet oiler involved extensive work. Not only did gear for refueling at sea need to be added, but also the capability to carry other types of fluids, such as gasoline for planes and boats, diesel for submarines, and even lubricating oil in drums on deck. Radios, boats, and navigation gear needed to be brought up to naval standards. Steaming with the fleet also required a strong suite of AA guns, with Cimarron being fitted with 4 5"/38 guns, 4 twin 40mm Bofors and 4 twin 20mm Oerlikons. The 5"/38s were accompanied by a Mk 37 director, giving her the same medium gun battery as a prewar destroyer.⁵ The pressures of war meant that the battery was soon reduced to a single 5"/38 and four 3"/50s with a simple director. All of these guns took extra crew. A Cimarron in civilian service had a design crew of only 69, while the same ship in naval service at the end of the war had accommodations for 301.

Oiler Neches refueling destroyer Sands

The importance of fast auxiliaries and being able to fuel quickly at sea was demonstrated by the first major operation of the Pacific War, the attempted relief of Wake Island. The task force charged with delivering reinforcements was first slowed by the 12.5 kt speed of the accompanying oiler Neches, then rough seas, inadequate gear⁶ and inexperienced crews meant it took two days to refuel the escorting destroyers. In the end, this delay sealed Wake's fate.⁷ Later on, the same techniques were critical to the success of the Doolittle Raid.

USS Rushmore comes alongside HMAS Success

These sorts of problems were soon overcome, and underway replenishment⁸ soon became a routine, if still somewhat tricky, operation. Today, it is still practiced in the same basic form, although there have been developments in technique.⁹ It begins with the oiler on a constant course at a steady speed. The ship to be refueled moves to a station a few hundred yards behind the oiler, and waits for its turn. On a signal, it slowly begins to overtake, staying a hundred feet or so clear of the other ship's side. This process takes 5-10 minutes.

A shotline being fired between ships

The really tricky bit comes as the two ships get close, and the water flowing around their hulls starts to interact. When steaming side-by-side, the effect pulls them together, getting stronger as they get closer. Careful shiphandling, done almost entirely by eye, is required to avoid a collision. At 12 kts, slightly slower than typical replenishment speed, a 1° difference in heading produces a lateral speed of 20 ft/min. The process ends with both ships alongside each other and at the same speed. During the early part of WWII, separation was often 50' or less, while modern equipment allows separation to be around 160'.

Hoses being pulled across from Cimarron to Enterprise, 1944

The first line, known as the Phone & Distance (P&D) Line, is fired across by a line thrower. This line is marked with flags every 20', making station-keeping much easier, and allows the bridge crews to talk to each other.¹⁰ After the P&D line is secured, the shotlines for the replenishment equipment follow. These are light lines, to which heavier messenger lines are attached and hauled over. These in turn allow the even heavier spanwires, which support the hoses, to be hauled across the gap between ships.

A fuel probe is hooked up

Multiple hoses are often sent across at this point, to allow faster fueling. Elaborate mechanisms onboard the oiler ensure that the spanwire is properly tensioned despite the movement of the two ships. Modern refueling rigs can support a variation of about 40' on each side of the 160' mark, and include automatic disconnects for the hoses if the tension becomes too great. During WWII, men with axes were used instead.

Diagrams of modern STREAM UNREP gear (top) and WWII-era close-in rig (bottom)

Once everything is hooked up, the two ships and their crews have to maintain their separation while the fuel flows. Modern equipment allows up to 180,000 gallons per hour to be pumped through each hose, although the situation in WWII was somewhat worse.¹¹ At one point during WWII, the oiler Platte steamed next to Enterprise for 5.5 hours at night, separated by only 50'.

USS Mispillion refueling USS Bennington

When replenishment is completed, the hose is hauled back aboard the oiler, and then the spanwire is cast loose by the receiving ship. At this point, USN ships traditionally play breakaway music, a song that usually has some relation to the ship. Famous examples include the use of the Star Trek theme by the USS Enterprise and the William Tell Overture by Ranger. For ships without such an obvious connection, the song is chosen by the Captain.¹²

USS San Jacinto performs an emergency breakaway from oiler Big Horn

If things go smoothly, the breakaway is the easiest part of the UNREP, as the receiving ship merely has to steer away and increase speed slightly. If they don't, an emergency breakaway may be called for. That involves trying to get the ships as far apart as possible, which is somewhat more exciting.

Iowa, a destroyer and an oiler off Korea

But despite all the development work, oilers alone weren't enough to support a war against Japan. Forward bases would be needed, and to make them mobile, most of the facilities had to be aboard ships. And to keep the fleet at sea even longer, the last year of the war saw the USN develop techniques to transfer ammunition and supplies at sea as well.