YANGON • Captain Tun Myat Aung leaned over the hot pavement in Yangon, Myanmar's largest city, and picked up bullet casings. Nausea crept into his throat. The shells, he knew, meant that rifles had been used - real bullets fired at real people. That night, early this month, he logged on to Facebook to discover that several civilians had been killed in Yangon by soldiers of the Tatmadaw, as Myanmar's military is known.

Days later, the captain from the 77th Light Infantry Division, notorious for its massacre of civilians across Myanmar, slipped off base and deserted. He is now in hiding.

"I love the military so much," he said. "But the message I want to give my fellow soldiers is: If you are choosing between the country and the Tatmadaw, please choose the country."

The Tatmadaw, which says it has a standing force of up to a half million men, is often portrayed as a robotic rank of warriors bred to kill.

Since ousting Myanmar's civilian leadership last month, setting off nationwide protests, it has killed more than 420 people and assaulted, detained or tortured thousands of others, according to a monitoring group.

Last Saturday, the deadliest day since the Feb 1 coup, security forces killed more than 100 people, according to the United Nations. Among them were seven children, including a five-year-old boy.

Interviews with four officers, two of whom have now deserted, paint a complex picture of an institution that has thoroughly dominated Myanmar for six decades.

From the moment they enter boot camp, Tatmadaw troops are taught that they are guardians of a country - and a religion - that will crumble without them. They occupy a privileged state within a state, in which they live and work apart from the rest of society, imbibing an ideology that puts them above the civilian population.

The officers described being constantly monitored by their superiors, in barracks and on Facebook. A steady diet of propaganda feeds them notions of enemies at every corner, even on city streets.

The cumulative effect is a bunkered worldview in which orders to kill unarmed civilians are to be followed without question.

While the soldiers say there is some dissatisfaction with the coup, they regard a wholesale breaking of ranks as unlikely. That makes more bloodshed likely in the coming days and months.

"I joined the Tatmadaw to protect the country, not to fight our own people," said a captain who is a graduate of the prestigious Defence Services Academy, Myanmar's equivalent of America's West Point. His name is not being published because of the possibility of retribution; he is still on active duty.

"I am so sad to see soldiers killing our own people," he added.

The Tatmadaw has been on a war footing since the country gained independence in 1948, battling communist guerillas, ethnic insurgencies and democracy advocates forced into the jungle after military crackdowns.

The enemy can also be within. A target of the Tatmadaw's ire is Ms Aung San Suu Kyi, the civilian leader deposed and locked up in last month's coup. Her father, General Aung San, founded the Tatmadaw. Today, the Tatmadaw's foes are again domestic, not foreign: the millions of people who have poured onto the streets for anti-coup rallies or taken part in strikes.

Last Saturday, which was Armed Forces Day, Senior General Min Aung Hlaing, the commander-in-chief and instigator of the coup, gave a speech vowing to "protect people from all danger".

As tanks and goose-stepping soldiers paraded down the broad avenues of Naypyitaw, the bunker-filled capital built by an earlier junta, security forces across the country shot protesters and bystanders alike, with more than 40 towns seeing violence.

"They see protesters as criminals because if someone disobeys or protests against the military, they are criminals," Captain Tun Myat Aung said. "Most soldiers have never tasted democracy their whole lives. They are still living in the dark."

Although the Tatmadaw shared some power with an elected government over the five years preceding February's coup, it kept its grip on the country. It has its own conglomerates, banks, hospitals, schools, insurance agencies, stock options, mobile network and vegetable farms.

The military runs television stations, publishing houses and a film industry, with rousing offerings like Happy Land Of Heroes and One Love, One Hundred Wars.

There are Tatmadaw dance troupes, traditional music ensembles and advice columns admonishing women to dress modestly. The vast majority of officers and their families live in military compounds, their every move monitored. Since the coup, most of them have not been able to leave those complexes for more than 15 minutes without permission.

An officer who deserted after the coup said: "We have to follow every order of our seniors. We cannot question if it was just or unjust."

Officers' children often marry other officers' offspring or the progeny of tycoons who are said to have profited from their military connections. Often, foot soldiers breed the next generation of infantrymen.

In pre-dawn Yangon on Feb 1, Captain Tun Myat Aung clambered onto a military truck, half-asleep, strapping on his helmet. He did not know what was going on until a fellow soldier whispered about a coup. "At that moment, I felt like I lost hope for Myanmar," he said.

Days later, he saw his major holding a box of bullets - real ones, not rubber. He cried that night.

"I realised," he said, "that most of the soldiers see the people as the enemy."

NYTIMES