The current academic consensus is that there is no consensus.
Let's review.
There have been four major investigations into the sinking of the Maine:
The first took place in 1898, immediately after the sinking. The McKinley administration created a naval board of inquiry that concluded unanimously that the ship was sunk "only by the explosion of a mine situated under the bottom of the ship at about frame 18, and somewhat on the port side of the ship."
The second investigation took place in 1911. President Taft ordered the Army Corps of Engineers to study the wreckage. Never to do anything by halves, the Corps built a cofferdam around the ship's wreckage, pumped out all the water and examined the exposed hull. Hundreds of photographs were taken, and the Corps removed much of the wreckage. A revised board of inquiry reaffirmed that a mine sank the ship, but it concluded the mine had detonated at a different place.
The third investigation came in 1974, when Admiral Hyman Rickover, father of the nuclear Navy, asked historians to re-examine the case. The historians dredged Spanish archives and consulted with foreign militaries about their own experience with internal explosions. They consulted professional engineers to analyze the 1911 photographs and took into context the "natural tendency to look for reasons for the loss that did not reflect upon the Navy." This study resulted in How the Battleship Maine was Destroyed. That book concluded the explosion was, "without a doubt," internal.
The fourth investigation came in 1999 and was conducted by the National Geographic Society. NGS commissioned a study by Advanced Marine Enterprises, which conducted the first detailed computer modeling of the disaster. AME stated that a coal fire within a bunker could have raised the temperature within one of the Maine's magazines to hazardous levels within a few hours. As to a mine strike, AME found that even a simple mine consisting of 100 pounds of black powder and a contact fuse could have sunk the ship. "If so, the mine must have been perfectly placed, which under the circumstances would have been as much a matter of luck as skill.” While it did not discount either option for the Maine's destruction, AME ultimately concluded (based on the 1911 photographs) that there was more evidence in favor of the Maine's destruction by a mine.
Let's review the competing evidence for each side, and you can make up your mind.
For a mine detonation:
• The Maine carried a type of bituminous coal that rarely spontaneously combusted.
• Bunker A16 was not situated by a boiler or any other external heat source, and spontaneous combustion does not occur unless there is a heat source to speed up the process.
• When Bunker A16 was inspected the morning of the disaster, the temperature was only 59 degrees Fahrenheit.
• The Maine's temperature sensor system did not indicate any dangerous rise in temperature on the morning of the last inspection.
• Discipline on the Maine was excellent, and regular inspections of coal bunkers for hazards, as well as the implementation of precautions for preventing bunker fires, were diligently carried out.
• A number of witnesses stated that they heard two distinct explosions several seconds apart. If anything else besides a mine had triggered the magazine explosion, then witnesses would have only heard one blast, because the only explosion would have been that of the magazines.
• The only reason that two explosions would have been heard is if something besides the magazine had exploded, such as a mine.
• Divers who examined the bottom plates of the Maine reported that they were bent inward. This was subsequently confirmed with 1911 photographs.
• Divers spotted a large hole on the floor of Havana harbor, something that would not have occurred with a magazine explosion. Those are directed upward, toward the path of least resistance.
For an internal explosion:
• Spontaneous combustion of coal was a fairly frequent problem on ships built after the American Civil War. Coal was exposed to air, oxidized and began burning. The heat was transferred to the ship's magazines, causing an explosion.
• The Maine's bituminous coal was more subject to spontaneous combustion than anthracite coal. Furthermore, higher moisture content increases the danger of spontaneous combustion. The Maine had spent most of the previous three months in Key West or nearby, where tropical moisture predominates.
• Bunker A16 had not been inspected since 8 a.m. The explosion occurred around 9:40 p.m. There was ample time (12 hours) for a coal bunker fire to smolder into a disaster.
• From 1894 to 1908, more than 20 coal bunker fires were reported on U.S. Navy ships.
• No one reported seeing a geyser of water thrown up during the explosion, a common sight when mines explode underwater.
• No one reported seeing any dead fish in the harbor and these would have been seen if there had been an external blast.
• Inward bending of the plates could have been caused by water displacement occurring at the same time the front of the ship was breaking away from the rear.
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Just to clarify, you took a high school history class where your instructor referred to it as a "false flag attack?"
Can you elaborate on what your instructor said? Did he or she use an actual history book referencing this? Or was it mentioned as a theory in passing?
I think it could be described as "mixed." In other words there is no consensus.
There have been a number of investigations into the incident. Officially both the Spanish and the U.S. did investigations in 1898, which came to different conclusions. In 1911 the U.S. removed it from the harbor, and took the opportunity to redo the investigation more thoroughly. And the evidence from these three investigations has been pored over for more than a century, with no definitive conclusion.
The general conclusion has always been the same; the reason the Maine sunk was that its main powder bunker exploded. But what set that off is what people argue about. And given the length and depth of the argument, it seems clear that no definitive answer exists. It could have been an accident, set off by the coal bunker. It could have been set off by a mine outside the ship. And yes, it could have been set off by a small explosive inside the ship.
But a false flag operation seems implausible to me. The McKinley administration already had enough support to go to war. In fact McKinley seems to be one of the last people to be in favor of war. And the Maine wasn't mentioned by McKinley as a Casus Bellus when he asked for a declaration of war. I suppose it is possible that one of the jingos in the U.S. created the incident to force McKinley's hand. Or it is possible that McKinley was so Machiavellian that he pushed he country to war, while appearing opposed. But that seems unlikely.
While somewhat dated now (it was written in 1976) How the Battleship Maine Was Destroyed by Admiral Rickover is the traditional go to for the subject.
Edited for spelling and to correct my slander of Admiral Rickover.
The Maine may not have suffered a boiler malfunction or an intentional attack [be it an external mine/torpedo or an internal act of sabotage].
There is a third possibility: Spontaneous detonation of explosives.
The USS Maine was equipped to fire armor-piercing shells from its big guns, and the explosive type used in these big shells was wet gun cotton. This is a type of high explosive which would have to be prepared for firing, and so warships had to carry a large amount of it on board in their magazines [a magazine in this context being a specially designed part of the ship where explosives & munitions are stored].
The volatile nature of gun cotton varies with temperature & humidity. Wet gun cotton ready for firing in an armor piercing shell is relatively inert. But this also means a warship that has traveled from say a cold part of the world to the equator or vice versa, is going to have to have its explosives on board monitored and serviced to keep it within a safe range of temperature & humidity. If some of the explosive falls into an unsafe range it can spontaneously detonate. Once that happens, the whole magazine can go off and destroy the ship fairly quickly.
Wet gun cotton was eventually phased out and replaced with things like fulminate of mercury, Maximite, Dunnite [aka Explosive D], Shimosa, cordite, and many other formulas. All of which were so close to each other chemically that there were some pretty intense legal battles over who had actually invented them & was worthy of being compensated with royalties.
I mention this because there is a famous incident that would give credibility to the idea that the USS Maine was destroyed by spontaneous detonation: The Japanese warship Kawachi. In 1918 the warship exploded. Like with the USS Maine, it happened quickly in the same forward-portion of the ship, resulted in the total loss of the ship, and much of the crew. And this was hardly a one-time only event. As Norman Friedman lists off in Naval Firepower (2013):
"At first, nitroglycerine made the new powders quite unstable. The French lost two battleships, Iena and Liberte, to their Poudre B. It was recognized as the culprit only in 1911, after a spontaneous powder explosion and fire on board a small boat carrying some of this powder away from a French battleship. Many other ships were lost to similar explosions; examples include the British HMS Vanguard (1917), the Italian Leonardo da Vinci (1916), the Russian Imperatritsa Maria (1916), and the Japanese Kawachi (1918) and Mutsu (1943). Wartime explosions were often attributed to sabotage at the time, probably largely to avoid raising safety questions in the minds of sailors aboard the surviving ships." [285]
Whether the US tribunal investigating the Maine believed it was spontaneous detonation or intentional malice, do you really believe they could have politically gone on out and publicly said that either, 1- They didn't actually know what happened, or 2- That it was an unavoidable consequence of using the high explosive formulas of the day [something that every ship in the navy had no choice but to carry]?
Suppose someone makes the argument that the Maine was destroyed in a so-called "false flag attack." At worst this would involve what, the United States somehow destroying their own ship, so they could use it as an excuse to fight a war with Spain? Yet when President McKinley went to congress to get authorization for fighting a war, the Maine was not used as a justification. Instead the actual argument consisted of the belief that Cubans needed to be allowed to self-govern. This is why the Teller Amendment stated that the United States would leave Cuba in event of Spain being defeated, instead of annexing the territory. If the loss of the Maine was required for getting into a war, you would expect it to be used as the justification for said war regardless how that destruction came about, wouldn't you agree?
Another problem, is that these warships were extremely important to national defense. The United States possessed a single battleship fleet, and it was usually in the Atlantic out of concern for the European powers. The United States lacked enough capital ships [that's the bigger warships] to protect both coasts. When Teddy Roosevelt put the capital ships on their famous white fleet tour around the world, this left both coasts of the country exposed to invasion. John Costello writes in The Pacific War (1982) that Kaiser Wilhelm had actually offered Theodore Roosevelt to put part of the German Imperial Navy off the Atlantic coast to protect it from aggression during the publicity stunt [TR turned the offer down].^1 The amount of time and cost it took to build every one of these larger warships, not to mention the political constraints on how many the Navy was given permission to build, all make the idea of destroying the Maine intentionally a very unsound one.
No one had anticipated that the United States would be able to defeat the Spanish at the Battle of Santiago Bay so easily [no warship lost versus 5], so going into the war the assumption was that every large warship was going to be extremely important, each playing a vital role with their biggest guns. The whole premise for the large warships was to make ships as heavily armored & heavily armed as possible, so that these extra big guns could fire armor piercing shells, which would poke a hole in the enemy ships causing them to quickly take on water and sink possibly after suffering a single good hit. That's what the academic theory was, on paper, in the academy. What really happened? Nothing at all like that. The US Navy destroyed the Spanish fleet using their mid-sized rapid fire guns. These guns, instead of sinking ships, were destroying everything above the hulls, causing them to catch fire & become disabled. The United States Naval Institute concluded that rather than phase out some of their mid-sized guns in favor of exponentially larger guns, they might want to return the 8-inch gun to service in future warships.^2 A complete 180 from what the established academic theory was. However, the addiction of supersized warships & their supersized armor piercing shells continued well into WW1, and debate whether that was a good idea is a whole other story.
Secondary question: Where are the remains of the USS Maine now?
Further to the excellent comments above, the French Navy suffered from a remarkable number of warship losses from spontaneous combustion of unstable ammunition, the same kind of propellant as the USS Maine used for her secondary armament. The battleships "Iena"and "Liberte" both blew up in harbour with the causes attributed to spontaneous ignition of propellant. There was also the loss of HMS Doterel at Punta Arenas, the Brazilian battleship "Aquidaban" at around the same period. Later examples, all attributed to spontaneous combustion of over-heated propellant, include HMS Bulwark, HMS Natal, IJNS Mikasa and IJNS Matsushima.
Does anyone know how many US ships the Spanish sank with mines during the war?
I'm confused here. If the hull plates were conclusively proven to be bent inwards, why is there any discussion about anything other than a mine being the cause? There's no possible way an explosion in the ship's interior could cause the hull plates to be blown inwards.