MAKHMOUR, Iraq - At the base of a rocky ridge rising from the surrounding farmland, the barrels of American artillery poke out from under camouflage covers, their sights trained on Islamic State-held positions.
Less than 10 miles from the front lines in the push toward the northern Iraqi city of Mosul, the U.S. outpost, known as Firebase Bell, is manned by about 200 Marines.
"Having them here has raised the morale of our fighters," said Lt. Col. Helan Mahmood, the head of a commando regiment in the Iraqi army, as his truck bumped along the dirt track that divides his base from the American encampment, ringed by razor wire and berms.
"If there's any movement from the enemy, they bomb immediately," he said.
The new firebase is part of a creeping U.S. buildup in Iraq since troops first returned to the country with a contingent of 275 advisers, described at the time by the Pentagon as a temporary measure to help get "eyes on the ground."
Now, nearly two years later, the official troop count has mushroomed to 4,087, not including those on temporary rotations, a number that has not been disclosed.
The troops are moving outside the confines of more established bases to give closer support to the Iraqi army as it prepares for an assault on the northern city of Mosul - putting them closer to danger.
That shift also comes at a time of political turmoil in Baghdad, which is threatening the legitimacy of Iraqi Prime Minister Haider al-Abadi, the key partner for the United States in its fight against the Islamic State in Iraq. Iraqi commanders said they are concerned that the crisis will complicate and slow progress on the battlefield.
It was inside Firebase Bell, a few miles outside Makhmour, a small mixed Arab and Kurdish town on the edge of Iraq's northern Kurdish region, that Marine Staff Sgt. Louis Cardin was killed on March 19 in a rocket attack, days after the Marines arrived here. His death was the second U.S. combat casualty in the war against the militants.
The area is prone to attack. Islamic State fighters sneak out at night to position explosives on the roads here and have sent a steady flow of suicide bombers to Iraqi army and Kurdish positions.
"One managed to infiltrate the base here," said Mahmood, pointing toward the main gate of his base, the headquarters of the Iraqi army's 15th Division, just a few hundred meters from Firebase Bell. The assault, which included five suicide bombers, also took place shortly after the Marines arrived, he said.
"We eliminated them," he said, adding that none of his own men were killed in the attack.
Before the U.S. troops and their M777 Howitzers moved here, the base came under regular fire.
A propaganda video released recently by the Islamic State showed a montage of clips of rockets and mortar rounds being launched toward the Iraqi army positions around Makhmour.
"I'm jealous of you because you are going to heaven," a militant said to a bearded fighter who was leaving for a suicide mission.
The attacks have since subsided, but Iraqi troops are still struggling to recapture the Islamic State-held village of Nasr, eight miles from the base, despite launching an offensive shortly after Cardin's death.
After an overnight battle, the Iraqi forces withdrew in order to avoid casualties, Iraqi commanders said.
The village was heavily rigged with explosives. The Islamic State sent car bombs.
"It was a fierce fight," said Mahmood, who like many of the other soldiers here was with the Iraqi army in Mosul when it collapsed so spectacularly two years ago. Since then, he has completed 41/2 months of training with the U.S.-led coalition.
He deemed the Nasr operation a success because dozens of militants were killed, even if the territory wasn't held. "My regiment isn't specialized in holding ground," he said. "We liberate and then withdraw."
Mahmood chuckled and shrugged when asked whether there were still no U.S. "boots on the ground" in Iraq, as President Barack Obama initially repeatedly pledged.
"They've become more active, and for us, it's had a positive result," he said.
But the battle for Nasr was a faltering first step for the 5,000 freshly trained Iraqi troops in Makhmour, and an indication of the level of hand-holding by U.S. forces that will be required as these forces move toward Mosul.
The Iraqi troops have recaptured a cluster of hamlets and villages in the vicinity of Makhmour, though reports were mixed on how heavy the Islamic State presence was there before the Iraqi advance.
In Kharbadan, one village they seized, bodies still lay rotting in the sun.
On a dusty track there, Iraqi soldiers pointed out other hamlets and clusters of mud buildings they had regained. The Iraqi army also said it had cleared nearby Mahana on Wednesday.
The inching gains have helped secure the base near Makhmour, but the Iraqi forces are heavily dependent on American firepower to move forward. U.S. artillery and airstrikes destroyed 30 or 40 Islamic State rocket and artillery positions in the area, said Maj. Gen. Najim al-Jabouri, head of Nineveh Operations Command, who is overseeing the buildup.
"They know very well it's not just the Iraqi army in the field," he said. "It's also the American air force and advisers with us, and artillery."
An operation for Mosul itself still appears distant, though. It will involve coordinating a mix of Sunni tribal fighters, Kurdish forces, Iraqi armed forces and Shiite and Christian militias, putting U.S. forces in the midst of a potentially drawn-out and complex battle for the ethnically and religiously mixed region.
Abadi, also commander in chief of Iraq's armed forces, faces the challenge of corralling them at a time when he is also fighting to steer the country out of its political crisis. Hundreds of protesters stormed parliament over the weekend demanding reform, in a major security breach.
Jabouri's own position is indicative of how politics can often complicate the battlefield in Iraq.
The commander, who was praised by then-President George W. Bush for his work to curb sectarian violence during the Iraq War, returned to the country last year after living in Virginia for eight years. He was directly appointed by Abadi, and his relationship with the Defense Ministry is openly fractious.
Jabouri admits that has caused "some problems."
"It's like a miracle here," he said. "Just the Iraqi army without any tanks, without any support, just from the American forces."
Unlike on other battlefields in Iraq, the army here is not supported by counterterrorism forces, the country's most elite troops, who have led the offensives for Hit and Ramadi. In any real push for Mosul, they'll be needed, Jabouri said. However, some of those already stretched special forces units have been recalled to the capital because of the problems there.
Jabouri hopes some tanks will arrive soon but is also in need of more troops, police and engineering units, he said.
The United States has said it will provide close air support from Apache helicopter gunships for Mosul, but that also puts pilots at risk of being shot down.
The battle will require coordination with the Kurdish regional government in the north, which has a strained relationship with Baghdad and complains that it lacks military support.
"There are political problems," said Mahdi Younis, a commander with the Kurdish peshmerga forces. "If they want us to participate, they should supply us like they are supplying the Iraqi army," he said of the United States, which currently supplies its military support to Iraq through Baghdad.
While Iraqi forces in Makhmour are equipped with U.S.-supplied M-16s, the peshmerga tote old Kalashnikovs.
Jabouri wouldn't give a specific timeline for the offensive but said it would be "soon," although even before the dramatic ransacking of Iraq's parliament Saturday, he expressed concern that the country's political crisis would have an impact.
"This has a big influence on us," he said. "It's a very, very tough crisis."
He used to speak to the prime minister every evening, he said, but hasn't now for a month. "He's very busy."