1974 Rickover investigation

Rickover became intrigued with the disaster and began a private investigation in 1974, using information from the two official inquiries, newspapers, personal papers, and information on the construction and ammunition of Maine. He concluded that the explosion was not caused by a mine, and speculated that spontaneous combustion was the most likely cause, from coal in the bunker next to the magazine. He published a book about this investigation in 1976 entitled How the Battleship Maine Was Destroyed.

In the 2001 book Theodore Roosevelt, the U.S. Navy and the Spanish–American War, Wegner revisits the Rickover investigation and offers additional details. According to Wegner, Rickover interviewed naval historians at the Energy Research and Development Agency after reading an article in the Washington Star-News by John M. Taylor. The author claimed that the U.S. Navy "made little use of its technically trained officers during its investigation of the tragedy." The historians were working with Rickover on a study of the Navy's nuclear propulsion program, but they said that they knew no details of Maine's sinking. Rickover asked whether they could investigate the matter, and they agreed. Wegner says that all relevant documents were obtained and studied, including the ship's plans and weekly reports of the unwatering of Maine in 1912 (the progress of the cofferdam) written by William Furgueson, chief engineer for the project. These reports included numerous photos annotated by Furgueson with frame and strake numbers on corresponding parts of the wreckage. Two experts were brought in to analyze the naval demolitions and ship explosions. They concluded that the photos showed "no plausible evidence of penetration from the outside," and they believed that the explosion originated inside the ship.

Wegner suggests that a combination of naval ship design and a change in the type of coal used to fuel naval ships might have facilitated the explosion postulated by the Rickover study. Up to the time of the Maine's building, he explains, common bulkheads separated coal bunkers from ammunition lockers, and American naval ships burned smokeless anthracite coal. With an increase in the number of steel ships, the Navy switched to bituminous coal, which burned at a hotter temperature than anthracite coal and allowed ships to steam faster. Wegner explains that anthracite coal is not subject to spontaneous combustion, but bituminous coal is considerably more volatile and is known for releasing the largest amounts of firedamp, a dangerous and explosive mixture of gases (chiefly methane). Firedamp is explosive at concentrations between 4% and 16%, with most violence at around 10%. In addition, there was another potential contributing factor in the bituminous coal: iron sulfide, also known as pyrite, was likely present. The presence of pyrites presents two additional risk factors, the first involving oxidation. Pyrite oxidation is sufficiently exothermic that underground coal mines in high-sulfur coal seams have occasionally experienced spontaneous combustion in the mined-out areas of the mine. This process can result from the disruption caused by mining from the seams, which exposes the sulfides in the ore to air and water. The second risk factor involves the additional capability of pyrites to provide fire ignition under certain conditions. Pyrites derive their name from the Greek root word pyr, meaning fire, as they can cause sparks when struck by steel or other hard surfaces. Pyrites were used to strike sparks to ignite gunpowder in wheellock guns, for example. The pyrites could have provided the ignition capability needed to create an explosion. A number of bunker fires of this type had been reported aboard warships before the Maine's explosion, in several cases nearly sinking the ships. Wegner also cites a 1997 heat transfer study that concluded that a coal bunker fire could have taken place and ignited the ship's ammunition.

1998 National Geographic investigation

In 1998, National Geographic magazine commissioned an analysis by Advanced Marine Enterprises (AME). This investigation, done to commemorate the centennial of the sinking of USS Maine, was based on computer modeling, a technique unavailable for previous investigations. The results reached were inconclusive. National Geographic reported that "a fire in the coal bunker could have generated sufficient heat to touch off an explosion in the adjacent magazine [but] on the other hand, computer analysis also shows that even a small, handmade mine could have penetrated the ship's hull and set off explosions within." The AME investigation noted that "the size and location of the soil depression beneath the Maine 'is more readily explained by a mine explosion than by magazine explosions alone'." The team noted that this was not "definitive in proving that a mine was the cause of the sinking" but it did "strengthen the case."

Some experts, including Rickover's team and several analysts at AME, do not agree with the conclusion. Wegner claims that technical opinion among the Geographic team was divided between its younger members, who focused on computer modeling results, and its older ones, who weighed their inspection of photos of the wreck with their own experience. He adds that AME used flawed data concerning the Maine's design and ammunition storage. Wegner was also critical of the fact that participants in the Rickover study were not consulted until AME's analysis was essentially complete, far too late to confirm the veracity of data being used or engage in any other meaningful cooperation.

2002 Discovery Channel Unsolved History investigation

In 2002, the Discovery Channel produced an episode of the Unsolved History documentaries, entitled "Death of the U.S.S. Maine." It used photographic evidence, naval experts, and archival information to argue that the cause of the explosion was a coal bunker fire, and it identified a weakness or gap in the bulkhead separating the coal and powder bunkers that allowed the fire to spread from the former to the latter.

False flag operation conspiracy theories

Several claims have been made in Spanish-speaking media that the sinking was a false flag operation conducted by the U.S. and those claims are the official view in Cuba. The Maine monument in Havana describes Maine's sailors as "victims sacrificed to the imperialist greed in its fervor to seize control of Cuba" and claims that American agents deliberately blew up their own ship.

Eliades Acosta was the head of the Cuban Communist Party's Committee on Culture and a former director of the José Martí National Library in Havana. He offered the standard Cuban interpretation in an interview to The New York Times, but he adds that "Americans died for the freedom of Cuba, and that should be recognized." This claim has also been made in Russia by Mikhail Khazin, a Russian economist who once ran the cultural section at Komsomolskaya Pravda, and in Spain by Eric Frattini, a Spanish Peruvian journalist in his book Manipulando la historia. Operaciones de Falsa Bandera. Del Maine al Golpe de estado de Turquía.

Operation Northwoods was a series of proposals prepared by Pentagon officials for the Joint Chiefs of Staff in 1962, setting out a number of proposed false flag operations that could be blamed on the Cuban Communists in order to rally support against them. One of these suggested that a U.S. Navy ship be blown up in Guantanamo Bay deliberately. In an echo of the yellow press headlines of the earlier period, it used the phrase "A 'Remember the Maine' incident."