SOME stared blankly down at the soil; others angled their furious gazes towards the sky. Sergeant Ricardo, a hulk-likespecialforces soldier clad in a pitch-black uniform, clasped his face in his hands and wept.

It was just after 1pm, and in a military graveyardinwesternRiodeJaneiro dozensofheavilyarmedpolicemen weremourningtheirlatestfallen comrade - Sergeant Wilson Sant'anna, 28, killed the previous day with a single rifle shot to the abdomen.

Minuteslater,theirvoicesechoed acrossthelushgreenhilltopswhich encircle the cemetery. "We the men of the special forces recognise our dependence on the Lord. Be with us when we look to defend the defenceless and to free the enslaved It is through the Lord that we fight and our victory belongs to you."

Life as one of Rio de Janeiro's 38,000 military police officers has never been an easy task, particularly for those whose mission it is to combat the city's three heavily armed drug factions, the Red Command, the Third Command and the Friends of the Friends or "ADA".

But a wave of police killings this year has underlined the growing dangers of law enforcement in this seaside tourist capital. More than 50 officers have now been executed or killed in the line of duty since January. The authorities, meanwhile, claim drug bosses are now ordering targeted assassinations of their men.

"The military police has never lost as many men as it is losing now," admitted Tenant Jorge Lobao, the chain-smoking head of Rio's Police Association, at the funeral of Sant'anna, who was 2007's 49th casualty. Lobao said he was offering a R$2000 (£500) reward for information that would lead to the killers.

The frontline of Rio de Janeiro's war on drugs is fought by Bope, the military police's special operations battalion. A meticulously trained elite force - feared and hated in equal measure in many of the city's 750 or so shantytowns - Bope is considered one of the world's leading urban Swat teams and has trained security teams from both the US and Israel.

If Bope are good it is because they have plenty of practice. And since Rio's governor, Sergio Cabral, came to power in January, there has been a significant rise in clashes between police and traffickers as the new governor attempts to restore order to the favelas, many of which have become autonomous zones controlled by heavily armed drug factions. The latest conflict, in a shantytown in northern Rio, has so far claimed 11 lives in just over a week, among them one Bope soldier.

Rio's special forces soldiers call themselves "the War Dogs". Virtually every day, they face the challenges of urban combat zones, street-to-street fighting in the narrow alleys of Rio's favelas. Although some criticise the use of the word "war" to describe Rio's cocaine-fuelled conflict, ask any Bope operative and he will tell you that is exactly what it is.

Last year, Rio de Janeiro was the scene of 6000 homicides, and around 1000 people are killed in shoot-outs with police each year.

Visitors to the Bope HQ, high in the mountain-tops over Rio, are left in little doubt as to the killing capacity of the War Dogs, whose coat of arms is a white skull with a dagger stuck through it.

Passing through the unit's gates, the visitor immediately comes across the most recognisable and daunting face of the Bope, the caveirao, or Big Skull - a black, tank-like bullet-proof vehicle with three small holes for snipers on each side.

Human rights group Amnesty International recently launched a campaign demanding that Rio's police take the caveirao off the streets, claiming that it had been used to kill indiscriminately and intimidate slum residents.

"He went to put the rubbish out and the caveirao shot at him," said Wilson Bonfim Santana, a bricklayer whose stepson was shot in the shoulder last week during the latest wave of violence. "His mother told him not to go out in the street, but the caveirao comes so quickly."

ForBopesoldiers,however,the caveirao is an essential piece of kit. "The bulletproof vehicle is used in defence of society and of the police," said the head of Rio's military police force, Colonel Ubiratan Angelo.

"Yesterday, for example, Bope soldiers were targeted by long-distance sniper shots which means they have no way of defending themselves," he said, referring to the previous day's operation in which a Bope soldier was killed. "It is a protective vehicle."

Cross over the frontline of this daily war between traffickers and military police and head into the back alleys of Rio de Janeiro's favelas and it quickly becomes clear why Bope soldiers are so desperate to hang onto the caveirao.

It is 7.30pm and the wind sweeps across a Third Command observation post at the heart of one of the favelas in the Bangu shantytown complex on the western outskirts of Rio.

Police intelligence suggests this area is home to the second biggest concentration of artillery in the city: an arsenal of around 200 rifles and 500 pistols in the hands of at least 200 traffickers, some as young as 11. Local drug bosses, meanwhile, boast that they possess landmines,bazookasandrocket-propelled grenades. Visit the favela and it doesn't take long to realise they are not exaggerating.

"The police are afraid of going in there," one local police inspector recently admitted to Rio's O Dia newspaper.

Up at the lookout post the six young boys on duty that night carry sub-machine guns, AK-47s and have a variety of hand grenades strapped to their waists. Their walkie-talkies repeatedly crackle to life, bringing updates from the favela's other "sectors". It is, as Bope soldiers are only too aware, a highly organised, military-style operation.

One of the local drug bosses - known as "Spider" - laughs off the idea that he might be scared of the Bope and points to the half-dozen "soldados" around him. To our left four teenagers lounge in a pick-up truck, scoffing takeaway McDonald'sdrinkingcartonsof coconut water and with three automatic FAL rifles poking out of the windows.

Behind them, on top of a small street-corner snooker table, a light machine gun isproppedonatripod.Thisisthe Minimi, a veritable weapon of war, produced - as the inscription on its barrel reveals-bytheBelgian"Fabrique Nationaled'ArmesdeGuerre".The weapon was used by US troops in the first Gulf war and can be found in the arsenals of the British, Canadian and Brazilian armies.

As if their firepower is not enough, Spider's men have also placed huge slabs of concrete in most of the favela's entrances to block out the caveirao.

"They the police come in here to kill, to kidnap residents," says Spider, trying to justify his arsenal. "If they didn't come in there would be no stray bullets at all."

"If it was up to me," he confesses later that night, "I'd only kill the cops."

A little after midnight, in another favela in the same complex, a toothless, 23-year-old drug boss nicknamed "The Player" is united with his troops in a street bar. He has a thick gold medallion around his neck and a black balaclava covering his hair. He lifts up his sports jacket, smiling his toothless grin, and pulls out a military-issue hand grenade.

"You want to see what I use when the Bope come in here?" brags the notoriously violent but seemingly personable trafficker, ordering one of his foot soldiers to bring him his weapon of choice.

Almost immediately a muscle-bound teenager marches into the bar, holding aloft a 7.62 assault rifle.

"It doesn't pierce the caveirao," the Player admits, taking a swig from a large glass of Ballantine's whisky and laughing. "But it certainly makes it wobble."

On the other side of town a dozen Bope officersmillaroundatoneofthe entrances to the Complexo da Penha, a sprawling network of slums in northern Rio. They are taking a break between their incursions into the slum to try and find the killers of Sant'anna.

Henrique Esteves, a police photographer from the Rio tabloid newspaper O Povo, is beginning his shift and is visibly sweating. "I feel like I'm in the middle of a war," he says.

Afewstreetsbehindhim,inthe middle of Vila Cruzeiro, one of Rio's most notorious shantytowns, is the exact spot where Sant'anna was gunned down two days earlier.

"I feel like a war correspondent. The only difference is that when I'm done here I go home and I'm with my family and everything is normal again."

It is 3.49pm when the soldiers finally pile into the caveirao and head at high speed back into the favela. Five minutes later, at 3.54pm, the rattle of gunfire fills the air once again.

"They're going up there to kill more people," screams one woman, whose son has just been admitted to hospital with bullet wounds.

Halfanhourlater,whenBope's caveirao emerges from the favela, the relief is stamped across the soldiers' faces. The men hug each other and wipe the sweat from their brows. They have been on duty since 5am and only one Bopesoldierhasbeeninjured- Alessandro Souza Pimenta, a 27-year-old who was admitted to hospital at around 10am with "abrasions resulting from grenade shrapnel" and has since been released. It has been a good day.

Not everyone has been so lucky. Inside the Getulio Vargas A&E, hospital director Carlos Chavez runs through a list of the day's victims - either those caught in the crossfire between the drug traffickers, Bope forces or those doing the shooting. The youngest victim is a three-year-old boy, whose mother was also injured, apparently with a rifle shot to the chest.

"There are rifle wounds, fragments from grenades, smaller calibre bullets, various types of wound," says Chavez .

Suddenly there is a screech of brakes and a battered VW minivan tears up in front of the hospital. Two men emerge from the vehicle grappling with a thick, bloodstained white duvet. A stiff pair of feet, speckled with blood and white paint, poke out of the end.

Chavez sighs: "More than 50 people have been shot since Tuesday night."

Back in the military cemetery, a black civil police helicopter plummets down from the blue sky and begins circling Sant'anna's grave, no more than five metresabovetheheadsofthe mourners.

Little by little, the sobs of the special forces soldiers transform into an angry, determined growl as they belt out the Bope anthem in tribute.

"At any time, at whatever cost, with extreme energy we combat all of our enemies," they bellow. "It is a relentless war fought by anonymous heroes. We are the special forces!"

Astheysing,Sant'anna'swidow collapses into a chair inside a white tent near the grave, while the soldier's grandmother buries her head in the chest of another relative.

"Only God can end this absurdity," she weeps. "To lose a kid that you have spent your whole life raising, all for nothing - I can't understand it."