What the three men were doing when they were ambushed has remained secret. The embassy later described the incident as an “ambush,” and authorities detained 14 federal police for suspected links to organized crime.

Somewhat uniquely, Mexico’s armed forces are divided into two separate Cabinet-level entities, with a naval secretariat overseeing the navy and a national defense secretariat in charge of the army and air force. The two secretariats rarely coordinate except on orders from the presidential office. They sometimes saw each other as foes.

“There were instances of shootouts,” said Richard Downie, director of the Center for Hemispheric Defense Studies at the National Defense University in Washington.

The navy has one advantage in keeping its force free of organized crime: Unlike the army, naval infantry units have no fixed inland bases. That mean navy officers are not exposed as much as commanders of army bases to the plata o plomo (money or death) demands of crime bosses.

“They go in and out on specific missions. They are not subject to the corruption that comes when you are somewhere for quite some time,” Downie said.

Naval infantry units now number about 15,400 out of total navy force of 56,000, Guevara said. Of those, special forces units make up a brigade, perhaps up to 1,800 men.

“Given these numbers, the budget they have, the personnel they can deploy, they’ve been doing quite well,” said Guillermo Vazquez del Mercado, an independent security analyst who once worked for Mexico’s National Security Council.

Attitudes within the navy and army differ dramatically. Naval officers routinely seek graduate degrees and interact with civilians, while army officers remain deeply hierarchical and insular, experts say.

Camp, the Claremont McKenna professor who has lectured at both the navy and army academies, said naval officers pepper him with questions while army officers stay silent. Camp said naval officers are four times more likely to study abroad than army officers.

Mexico’s navy sent a permanent rotating liaison to the U.S. Northern Command, the Colorado-based unified military command that overseas activities from Alaska to Mexico, in 2006, years before the Mexican army followed suit. The navy also has liaisons in Key West, Fla., and Norfolk, Va.

Neither Mexico nor the United States has explained what kind of assistance the CIA may be providing to the navy, or indeed the level of intelligence that is offered.

“It’s no secret that we operate (unmanned aerial vehicles) on the border. We do electronic intercepts. That’s in the public domain. What is secret is what we obtain and who we share it with,” said McCabe, of the U.S. Naval War College.

“There’s a lot of folks that just don’t trust the army with intelligence,” he added.

Painted as “risk averse” in leaked U.S. diplomatic cables, Mexico’s army has battled corruption allegations for years. In May, prosecutors rounded up three retired army generals and a lieutenant colonel, later charging them with protecting the Beltran Leyva drug cartel.

One of the diplomatic cables released by WikiLeaks last year excoriated the army for not acting on U.S. intelligence on the whereabouts of Arturo Beltran Leyva, who was holed up in a mansion in Cuernavaca close to an army base. A naval unit later went in and killed the drug lord.

Mexican experts said the naval intelligence unit is honing its own skills in analyzing and gathering information.

“It’s on its way to (being) recognized as the most successful intelligence agency in Mexico, although I would not discard the Federal Police intelligence capabilities,” Guevara said.