Why the USS Abraham Lincoln Rusted Above the Waterline and Not Below It

On the morning of 2 September the nuclear-powered aircraft carrier USS Abraham Lincoln eased alongside the pier at Laem Chabang, on the Gulf of Thailand, for the first real port visit of a deployment that began in San Diego the previous November. The photographs went around the world within hours. Long streaks of orange ran down the grey hull from the edge of the flight deck. The sponsons that hang off the sides were the colour of an old barn roof. A bright green ring of algae marked the waterline as neatly as a pencil line. The internet reached its verdict quickly: the United States Navy had let its most expensive warship rust.

We look at that photograph differently, because we spend our working lives selling the chemicals that make and unmake it. Rust is the single most common reason anyone buys phosphoric acid from us, and the pattern on the Lincoln’s hull is not a scandal. It is a diagram. The rust is exactly where a corrosion textbook says it should be, it is almost entirely absent where the textbook says it should be absent, and both the ship’s captain and a retired vice admiral were right to call it cosmetic. What follows is what the pattern means, why nine months at sea produces it, what the Navy actually spends fighting it, and what happens chemically when you take the fix — phosphoric acid — to a rusted piece of steel in a shop rather than a shipyard.

What the photographs actually show

The War Zone, which published the clearest set of images, described “running rust” and algae caked along the hull sides, a bright green algae ring at the waterline, and staining at the flight-deck edges and on the sponsons on either side of the ship. Every one of those locations is above the water. Below the waterline the hull is, so far as any photograph shows, its normal dark anti-fouling colour with a band of marine growth at the surface. That is the first thing to notice, and the whole article turns on it.

Asked about the ship’s appearance on the pier, her commanding officer, Capt. Dan Keeler, told the Associated Press that “it is normal for a long deployment” and declined to say more. Newsweek put the question to retired Vice Admiral Robert Murrett, who characterised the wear as consistent with an extended deployment and the missing paint as cosmetic rather than operationally significant. The same article carried the one caveat worth keeping: analyst William Freer noted that rust left unchecked long enough can eventually reach watertight seals and require shipyard work. Cosmetic today is a description of the present, not a promise about the future, and that distinction is where the chemistry comes in.

Rust is a battery. Seawater is the wire.

Iron does not simply “react with air.” Rusting is an electrochemical cell, and it needs the same three things a battery needs: a place where a metal gives up electrons, a place where something accepts them, and a conductive path between the two.

At the anode, iron atoms in the steel dissolve as iron(II) ions and leave two electrons behind in the metal. At the cathode, somewhere nearby on the same surface, dissolved oxygen takes those electrons and, with water, becomes hydroxide. The iron(II) ions and hydroxide meet in the water film, precipitate, and oxidise further in air to the hydrated iron(III) oxides we call rust. Written out:

The conductive path is the water sitting on the steel. In rain, that water is a poor conductor, which is why a steel fence in a dry inland town lasts for decades. In seawater it is an excellent one. NOAA puts the salt content of seawater at about 35 parts per thousand, and names chloride and sodium as the two most prevalent ions dissolved in it. A film of that on a hull is not a puddle; it is an electrolyte, and the anode and cathode on the steel can be centimetres apart and still complete the circuit easily.

Chloride does a second, nastier job. Clean steel in air grows a very thin, tightly bonded oxide skin that slows further attack; it is the reason a bare machined part in a dry shop stays bright for weeks. Chloride ions penetrate and break down that skin, and once a pit has started they concentrate inside it and keep it acidic and active. That is why the same hull with the same paint can shrug off a Texas summer and streak within weeks at sea. Nothing about the steel changed. The wire did.

The splash zone: the worst address on the ship

If seawater were the whole story, the hull below the waterline would rust fastest, because it is wet all the time. It does not, and the reason is oxygen. A submerged plate is bathed in an electrolyte, but the oxygen that drives the cathode reaction has to diffuse to the steel through the water, and the water near the surface is already depleted by everything else consuming it. Submerged steel corrodes, but slowly and evenly, and anti-fouling paint plus the Navy’s cathodic protection systems slow it further.

Just above the waterline, everything is different. Corrosion engineers call this band the splash zone, and it is the most aggressive environment a marine steel structure sees. Field exposures of steel piles along the US Atlantic seaboard in the 1940s and 1950s — the classic work of Humble, LaQue and Larrabee — produced the same profile in every study: the peak of metal loss sits just above mean high water, and the profile has been reproduced in harbour and offshore work ever since. Three things happen there at once.

The splash band gets the three ingredients of the cell delivered in their most effective form. The water film is thin, so oxygen reaches the steel almost instantly instead of diffusing through a metre of seawater. The film is constantly renewed, so the cathode never runs short. And when it dries, the chloride does not leave; it stays on the surface as a crust, so the next wetting starts with a brine more concentrated than the sea itself. A 2021 study of steel in a simulated splash-zone environment put it plainly: high concentrations of dissolved oxygen, sufficient light and wind waves cause serious corrosion on the surface of steel structures exposed to seawater there.

Now look at the carrier again. The rust is heaviest on the hull sides from a few metres above the water up to the deck edge, on the sponsons that overhang the water and catch every wake, and at the flight-deck lip where spray is thrown highest. That is a splash-zone map. The clean hull below the green algae ring is the immersed zone behaving exactly as it should.

Why the Navy cannot simply paint it at sea

The obvious question is why a crew of several thousand did not keep up with the paint. The answer is that they did what could be done, and the rest requires a pier. Ships are preserved in port: the hull sides are reached from the pier and from boats, the coating is applied in controlled conditions, and it is given time to cure without being hit by spray. At sea, especially during sustained high-tempo operations, the crew can chip and touch up what they can reach from the deck, and not much more. The War Zone made the same point in its coverage of the Lincoln: there is only so much that can be done out of port when every resource is on operations.

The Lincoln is not the first ship to come home looking like this, only the longest at sea. In October 2020 the destroyer USS Stout returned to Norfolk after 215 consecutive days without a port call, a record at the time, having covered more than 60,000 miles, and she was streaked and battered in exactly the same way. Pandemic restrictions had made port visits unsafe, so the crew completed the first modern mid-deployment repair period at sea and simply could not do the topside preservation that normally happens pierside. The Stout broke a record of 206 days held jointly by the carrier USS Dwight D. Eisenhower and the cruiser USS San Jacinto. The Lincoln has now passed all of them by more than two months.

Nor is the pattern new to the Navy’s own leadership. When a run of rusty destroyers drew comment in 2021, a spokeswoman for U.S. Naval Surface Forces, Cmdr. Nicole Schwegman, told Task & Purpose that “the harsh environment in which we operate degrades our ships, and our sailors work hard to address corrosion along with all the maintenance and crew training required to sustain our Navy’s warfighting readiness.” A defence analyst quoted in the same piece, Becca Wasser of the Center for a New American Security, was blunter: if you want to address rust on ships, the answer is operating less and maintaining more.

The money confirms it. The Department of Defense’s Corrosion Policy and Oversight Office measured the cost of corrosion across the services and found that Navy ships alone cost $3.3 billion a year to protect and repair from corrosion in fiscal years 2008 through 2010, which was 21.6% of all ship maintenance spending. Across the whole department the figure was $23.3 billion a year, about a fifth of the maintenance budget. NAVSEA told Naval News in 2023 that topside coatings have moved from silicone alkyds to polysiloxane systems with longer service life, and that modern tank coatings first applied in the early 2000s have kept many tanks corrosion-free for 15 to 20 years. Better paint has stretched the interval between preservation periods. It has not removed the need for a pier.

The acid named for the job: what Naval Jelly actually is

Ask anyone who has ever cleaned up a rusty tool what they used and a fair share will name the pink gel in the plastic bottle. Its own safety data sheet is short on mystery. Loctite Naval Jelly Rust Dissolver lists two hazardous components: phosphoric acid at 10 to 30% and sulfuric acid at 0.1 to 1%, carried in water with a thickener so it clings to a vertical surface. The Department of Transportation shipping name on the same document is simply “phosphoric acid solution.” Strip away the gel and the brand and you have a phosphoric acid solution at roughly the concentration we sell by the quart and the gallon as a rust remover.

Phosphoric acid earns its place for two reasons that most other acids cannot match at once. First, it dissolves rust. Iron(III) oxide is basic enough to react with the acid, and the reaction pulls the oxide off the surface as soluble iron phosphates and water:

Second, and this is the part that makes it a conversion treatment rather than merely a cleaner, once the loose rust is gone the acid reacts with the bare iron underneath and leaves a thin, tightly adherent layer of insoluble iron phosphate on the metal. That layer is grey, slightly crystalline and a poor conductor of electricity, which matters because a poor conductor makes a poor cathode. It is also microscopically rough, which is why it has been used for decades as the pre-treatment under paint: primers key into it. A phosphated surface is not rust-proof, and it will rust again if left bare in the weather, but it buys time and gives the coating a far better start than bare polished steel.

Concentration is a trade-off between speed and control. A 30% solution works in minutes to tens of minutes on light and moderate rust and is slow enough that it does not aggressively attack the sound steel beneath, which is why both the gel product and our own rust-remover grade sit there. Our 85% technical grade is the concentrate for shops that mix their own dip tank or want a stronger solution for heavy scale, and it should be diluted before it goes anywhere near a part; a ratio of roughly one part 85% acid to two parts water lands close to the 30% working strength. Add acid to water, never the reverse.

For the full head-to-head, including where oxalic acid genuinely beats phosphoric, our comparison Rust Removers Ranked goes through all five acids we sell by mechanism, speed and metal safety. It does not put our own rust-remover grade first in every case, because the chemistry does not.

Doing it in a shop, not a shipyard

Preservation on a 100,000-ton hull is a mechanical job: needle guns and blast media take the topsides back to bright metal before any coating goes on. On a trailer frame, a tank, a set of structural members or a truck bed, the acid does most of the work. The sequence that gives phosphoric acid the best chance is the one below; our complete guide to phosphoric acid rust removal expands each step.

1. Degrease first. Acid does not go through oil. Wash with a detergent or solvent degreaser and rinse, or the treatment will be patchy wherever the film was.
2. Knock off the loose scale. A wire brush or scraper removes the flaking layer so the acid reaches the adherent rust beneath instead of being spent on debris.
3. Apply 30% and keep it wet. Brush or spray the solution on and do not let it dry; a dry surface stops reacting. Ten to thirty minutes is typical for light and moderate rust. On vertical surfaces work in sections, or thicken the solution, which is the whole reason the gel product exists.
4. Rinse and dry fast. Rinse with clean water and dry immediately with compressed air or rags; the freshly phosphated surface is grey and slightly matte. Standing water on it undoes the work.
5. Prime within hours. The conversion layer is an anchor for paint, not a finish. In humid air, bare phosphated steel begins to discolour within a day.
6. Handle the rinse water responsibly. It is dilute acid carrying dissolved iron. Follow the local rules for your drain or collect it for neutralisation.

What the search data says about the photographs

A news story about a warship is not obviously a story about anyone’s trailer. The search data says otherwise. Interest in the ship itself spiked on 3 September and had faded almost to nothing within a week, which is how news behaves. Google Trends interest in the plain question how to remove rust in the United States, by contrast, roughly tripled between 2 and 8 September against its late-August baseline and was still elevated on 10 September. People saw the pictures, looked at something orange in their own yard, and went looking for the chemistry.

Common questions

Why is the USS Abraham Lincoln rusty?

Because it spent 286 days at sea without a liberty port, and the hull-side preservation that normally happens pierside could not be done. Steel in seawater corrodes electrochemically wherever the coating is breached, and the splash zone just above the waterline is the most aggressive band on any marine structure. The captain called the appearance normal for a long deployment, and a retired vice admiral told Newsweek it is cosmetic.

Why is the rust above the waterline and not below it?

Below the waterline the steel is continuously wet but oxygen has to diffuse through the water to reach it, so corrosion is slow and uniform and cathodic protection helps. Just above the waterline the steel is wetted and dried repeatedly, each wetting delivers a thin oxygen-saturated film, and each drying leaves concentrated salt behind. Field studies since the 1940s put the peak of metal loss just above mean high water.

Is the rust on a Navy ship a structural problem?

Running rust is a stain on the paint plus a thin oxide layer at the breach; it is not a measure of steel lost. At published splash-zone rates even fully bare steel would lose well under a millimetre in 286 days, and hull plate is measured in centimetres. The parts that matter first are seals, hatches and fittings, which is why the ship will be preserved in port rather than left.

What is Naval Jelly made of?

Its safety data sheet lists phosphoric acid at 10 to 30% and sulfuric acid at 0.1 to 1% in water with a thickener, and gives the shipping name “phosphoric acid solution.” The gel exists so the acid clings to vertical surfaces and stays wet long enough to work.

How does phosphoric acid remove rust?

It reacts with iron(III) oxide to form soluble iron phosphate and water, lifting the rust off, and then reacts with the bare iron beneath to leave a thin grey layer of insoluble iron phosphate. That layer is a poor electrical conductor and a good anchor for primer, which is why phosphoric acid is used as a paint pre-treatment as well as a rust remover.

Should you use muriatic acid to remove rust from steel?

Not on steel you intend to keep. Hydrochloric acid removes rust quickly but leaves chloride behind, and chloride is the ion that drives marine corrosion in the first place. Imperfectly rinsed parts flash-rust within hours. Phosphoric acid for steel that will be painted, oxalic acid for rust stains on other surfaces, and muriatic acid for concrete.

The three we would put on the bench

Phosphoric Acid 30%, Technical Grade

The Naval Jelly strength, without the jelly. Dissolves rust and leaves the phosphate base for primer.

Phosphoric Acid 85%, Technical Grade

The concentrate for shops that mix their own bath. Dilute before use; acid into water.

Oxalic Acid Dihydrate, Technical Grade

For the stain, not the scale: rust marks on gelcoat, wood, concrete and non-ferrous metal.