Professional Note: A Destroyer Guy Discovers LHDs

I had been a destroyer guy my whole career until major command. Therefore, I was surprised to find myself slated to USS Essex (LHD-2), having no background in complex flight operations or working with Marines and assault craft of various kinds, and only vague 20-year-old recollections of steam engineering basics. Most important, I had never driven large ships.

LHDs are large, imposing ships up close. My initial thought, upon visiting a sister ship in the training pipeline was, "How am I ever going to learn to drive a ship this big?" This was followed closely by, "Well, tugs will take care of everything in close, and the rest will just be mostly driving in straight lines."

The latter preconception turned out to be wrong. LHDs are remarkably handy and tun to drive. My first hint of this came during the simulator practicing a man overboard drill. The obvious answer, I thought, was go "all stop" and launch a boat or search-and-rescue helo because, of course, it would take forever to turn around and pick up the man. After suitably rude urging by the instructor. I did a standard Anderson turn and was startled to see how rapidly the simulated LHD turned.

Of course, that was only a simulation (though the MSI simulator turned out to be remarkably high-fidelity). The real test and learning for my new senior officers and me came in taking the Essex out the first time before receiving our Marine air combat element (ACE) on board, and trying out a wide range of speeds and rudder angles on a calm sea to see how she behaved under various circumstances. To say we were impressed is an understatement. In essence, we found we could drive her pretty much like a destroyer.

The Wasp-class LHDs are 844 feet long. 106 feet wide (222 with elevators), and draw about 28 feet. They have about 80,000 shaft horsepower, roughly that of a destroyer, but they displace some 44.000 tons, depending on cargo and liquid load, and they do not have controllable reversible propellers (CRPs).1 A typical Marine ACE includes 25-30 helicopters of various kinds and 4-6 Harrier vertical or short take-off and landing jets, complemented by 2-4 Navy MH-60S helos. Alternatively, the LHDs can carry as many as 25 Harriers.

The LHDs alternate surface and aviator commanding officers. By various accounts, both types tend to drive their big decks in a rather cautious fashion, likely because of preconceptions about big ships not being maneuverable and concerns about flight deck heel with aircraft on board.

In terms of heel, our air boss was comfortable with heels of up to 6° with aircraft moving on deck and up to 12° with all aircraft securely tied down. When moving heavy helos (e.g., CH-53s) athwartship, we would not exceed 4° of heel, because the small wheels of the tow tractor supply the only braking power.

The LHDs turn out to be highly stable platforms. After testing various combinations of speeds and rudder angles, we tried full speed/full rudder turns. Try as we might, we could not get the ship to heel more than 10.5° in low sea states, and generally she stayed well below 6°.

Because of apparent concern about heeling some use a formula such as "Rule of 25"-i.e., the combination of speed and rudder angle cannot exceed 25. We have found such thumb rules to be greatly over cautious. Moreover, such rules exact significant operational penalties in their application.

During flight operations, primary launches and recovers aircraft after the bridge gives a "green deck," during which the bridge is not free to maneuver except with explicit permission from primary for obvious reasons of aircraft safety. However, the bridge periodically needs to maneuver to chase the wind or adapt to the differing wind envelopes for different aircraft. To enable the ship to carry out the air plan efficiently, there must be close and rapid communication between bridge and primary. To ensure this, our policy is that primary immediately surrenders the green deck if it is not required and, in exchange, the officer of the deck (OOD) maneuvers the ship briskly into the wind (Fox Corpen) if/and as required, so as to minimize the time to go to green deck when needed.

A high-tempo LHD air plan tends to be rather rigid, especially when flying both helos and Harriers in a cycle. Several minutes' delay in getting an event done often has cascading effects. Harriers have a complex formula dealing with environmental conditions, engine condition, and fuel/weapons loads for each jet for each flight. A delay of just a minute or two in heading into the wind may require a significant delay to top off fuel, which in turn may impact other launch/recovery events.

This premium on brisk maneuvering under routine circumstances becomes even more important in the event of aircraft emergencies, when operating in geographically confined areas, or while conducting flight operations in heavy seas. OODs -should be ingrained with the imperative for routine brisk maneuvering-so that they can do it when they have to.

The Essex can do up to a 180° course change from any starting conditions in under 5 minutes while not exceeding the heel limitations noted above. Starting at slow speeds (5 knots or less), a "20/20" turn-20 knots rung up and 20° rudder angle-will result in the ship turning rapidly with very little heel, and emerging from a 180° turn with about 12 knots of speed over ground. Desired speed on the new Fox Corpen can be ordered about 30°-40° before the ship is on a steady course. Do not take off the full rudder too early or the turn will stall. A "20/30" turn-or 20 knots rung up and full rudder applied-will tighten the turn significantly, while the speed will remain below about 8 knots throughout. The turning radius in these turns will be less than that of a destroyer!

At fast speeds (>20 knots), any more than 2°-3° of rudder can cause the ship to heel to up 6°-7°. (There is not that much difference in heel whether one uses 5° or 15° of rudder, though the rate at which max heel is achieved differs.) We use basically the same "carrier turn" that carrier OODs are trained to use. The sequence is "all engines stop," "all engines back two-thirds," "all stop," and "left/right full rudder" once speed falls below 13 knots, and then the desired ahead bell about halfway through the turn. The OOD can even put on 2°-3° of rudder when ordering the initial speed reduction, but that will increase the turning radius somewhat. The heel will level off at 4°-5°, then gently fall off. (Note: A starboard turn generally results in less heel than a port turn because of the island's location.)

For lesser turns in low sea states, full rudder turns result in heels of 4°-5° at 20 knots. It will feel somewhat alarming when a new commanding officer first tries this, but we have found that the maximum heel consistently remains within those limits.

These turns work reliably in low sea states. In higher sea states, it is even more important to turn as rapidly as possible during flight operations to minimize the time spent in the troughs or. with high waves, swells come in on the quarters. There is the possibility of heel from the turn being aggravated by a badly timed swell. If the heel starts to increase markedly from its 4°-5° amount, immediately go rudder amidships or even put on some opposite rudder. Once settled out, resume the turn. Do not increase the amount of rudder in the middle of these turns, because that will lead to excessive, possibly dangerous, heel.

We execute replenishment-at-sea break-aways in the same manner as destroyersi.e., 22 knots and full rudder once the stern is clear (though without the same rapid acceleration as gas turbine ships), and heel a maximum of 5°-6°. By the time we open enough to put full rudder on, speed generally is already up to 16-17 knots, and the result is a higher heel than in the turns described earlier.

Then there is stopping. The LHDs have a surge rate of about 60-65 yards per knot of relative speed in a speed range of about 12-22 knots. Below these speeds, they keep going and going unless a backing bell is applied. A one-third backing bell is essentially worthless. Even a two-third backing bell takes considerable time to take effect because, unlike the aircraft carriers, the shafts must be physically stopped and then reversed, but unlike the carriers, steam cannot be applied to ahead and astern turbines simultaneously.

When going from an ahead bell to a backing bell to slow down, the propulsion shafts generally do not change revolutions per minute at the same rate. Thus, when slowing rapidly by backing down from higher speeds, there is a pronounced yawing, which is potentially dangerous in tight waters. One other way to knock down speed rapidly is to cycle between right and left full rudder in a manner analogous to an aircraft sideslipping in order to take off speed.

Man overboard maneuvers are done in similar fashion to destroyers, except that stopping distance must be kept in mind. In an Anderson turn, putting the rudder over full while coming up to 20 knots will knock down the speed rapidly, while the thrust from the full bell will help keep the stern swinging quickly. It is important to cut the inboard engine promptly about one-third of the way into the turn both to tighten the turn and prevent excessive speed from building. For both Anderson and Williamson turns, once pointing more or less fair toward the man in the water, fishtailing the rudder as above will knock down speed, though of course it will be important to control the head as the man is approached. A properly handled LHD should be able to give some destroyers a good run for their money in doing a shipboard recovery.

So, why the emphasis on driving an LHD like a destroyer, other than to avoid being called an "Argentinian beef barge"?2 The key reason is so we can do it if we must in an emergency. There are other reasons as well, however. The style of driving arguably also sets the tone of the ship. An aggressive, brisk way of operating gets reflected in many of the other things a ship does and in the way her officers carry out their other duties. The "we can do anything" attitude is infectious and the resultant self-confidence has endless positive ripple effects.

All that said, new LHD commanding officers, especially those with no experience driving large ships, should try these various maneuvers with their own ships first, and ensure they are thoroughly comfortable with them. Do try this at home.

The amphibious warfare community has suffered unfairly and needlessly over the years from perceptions of being plodders. No doubt some of this misperception stems from overcautious shiphandling. This brings me to the final reason for driving an LHD like a destroyer: it is fun!