MEXICO CITY -- When a naval unit recently gunned down the leader of the feared Los Zetas crime group, the clash took place in the dusty town of Progreso, 70 miles from the Texas border and hundreds of miles from any ocean, indeed, far from any area where one would expect a modern navy to operate.

But these days, Mexico’s navy is active deep inside the country’s interior, eclipsing the army as the go-to security force in the country’s war on organized crime. It is a transformation that not only highlights Mexico’s peculiar defense organization – which provides the navy its own ministry – but also highlights how the United States has worked to find dependable allies in its campaign to stop drug trafficking.

The navy’s rise is not without political risk, however. As the navy outshines the 200,000-member army, politicians supportive of the army could well move against it, even though several senior retired generals were arrested earlier this year for alleged links to organized crime.

“There is an inter-service rivalry, and I think it’s accentuated by the success of these navy elite units,” said Roderic Camp, a Mexico scholar at Claremont McKenna College in California and author of a book on the Mexican military. “There’s no question that it’s creating tension between the army and the navy.”

For decades, the navy was relegated to protecting Mexico’s offshore oil platforms and patrolling its two ocean coastlines. Its unit of marines was a token amphibious force, and in a strange overlap, it vied with five army amphibious groups.

Then, in 2007, as Mexico’s drug war raged, Mexico’s congress enacted legislation that, in the words of Mexican security analyst Inigo Guevara Moyano, allowed the navy “to operate throughout the country, even in landlocked areas.”

“Some landlocked states, such as Aguascalientes and Zacatecas, have asked specifically for the presence of the marines during times of crisis,” Guevara said.

Actions in recent weeks underscore how the navy has taken the lead in Mexico’s war on crime, beginning with the arrest Sept. 12 in Tamaulipas state of Eduardo “El Coss” Costilla, one of the top leaders of the Gulf Cartel. Two weeks later, naval units captured Ivan Velazquez Caballero, a commander of the Los Zetas crime organization so brutal that he was known as “El Taliban.”

Then on Oct. 4, marines captured Salvador Alfonso Martinez, a Zetas commander known as “The Squirrel.” Three days later, on Oct. 7, a naval unit struck the heaviest blow against drug traffickers since President Felipe Calderon took office in late 2006, killing Heriberto Lazcano Lazcano, the founder and head of Los Zetas, apparently as he watched a baseball game at Progreso.

Curiously, despite its successes, the navy shies from foreign media. Its spokesman has declined since 2010 to speak to a McClatchy reporter, saying through an aide that he is too busy to answer questions.

“The navy is very sensitive to the fact that they are small and not as politically powerful as the army,” said Laurence L. McCabe, a professor of national security affairs at the U.S. Naval War College in Newport, R.I.

The navy’s close ties with U.S. agencies came to light Aug. 24, when Mexican federal police fired on a U.S. Embassy vehicle on a remote mountain highway. Two CIA agents and a Mexican navy captain were inside the armored vehicle, bound for a mountainside navy base.