US Apache attack helicopters and HIMARS rocket artillery systems will likely join 560 additional U.S. troops being sent to a northern Iraqi air base that Defense Secretary Ashton Carter said Monday would be used as a “springboard” to retake Mosul.

The AH-64 Apaches have already played a role in securing the air base outside the town of al-Qayyarah (also spelled Qayara) in the Tigris River Valley about 40 miles south of Mosul, Iraq’s second-largest city.

Last month, Navy Capt. Jeff Davis, a Pentagon spokesman, said that Apaches attacked and destroyed an ISIS VBIED (Vehicle-Borne Improvised Explosive Device) in al-Qayarrah, which was retaken by Iraqi Security Forces (ISF) over the weekend.

It was the first time the Apaches had seen action since the Islamic State of Iraq and Syria fighters swept into Iraq in June of 2014 against little resistance and threatened Baghdad.

Iraqi Prime Minister Haider al-Abadi had barred the use of the Apaches in the retaking of Ramadi and Fallujah in southern Anbar province but he has authorized their use for the long-stalled plan to retake Mosul, which Abadi has predicted will happen this year.

The truck-mounted M-142 High Mobility Artillery Rocket System (HIMARS) will also likely be placed at al-Qayyarah to support the retaking of Mosul. HIMARS systems have long been in place at the U.S. bases at the al-Asad airbase and in Taqqadum near Ramadi in Anbar province.

In a briefing to the Pentagon in April, Air Force Maj. Gen. Peter Gersten, deputy commander for operations and intelligence for Combined Joint Task Force-Operation Inherent Resolve, said the HIMARS system “absolutely” would move forward to northern Iraq once the ISF had secured a foothold near Mosul.

In Baghdad Monday on a one-day stop following the NATO summit in Warsaw last week, Carter said “I am pleased to report that today we agreed for the United States to bolster the Iraqi efforts to isolate and pressure Mosul by deploying 560 additional troops in support of the ISF at the Qayyarah West airfield.”

“With the retaking of Qayyarah West airfield, the Iraqi Security have once again demonstrated a serious will to fight,” said Carter, who questioned the will of the ISF to fight when Ramadi fell to ISIS in May 2015.

“This contingent of U.S. forces will help the Iraqis establish a logistical springboard for their offensive on Mosul, which Prime Minister Abadi re-affirmed to me he wants to accomplish this year,” Carter said.

Army Lt. Gen. Sean McFarland, who was wrapping up his leadership of CJTF-Operation Inherent Resolve, said he expected the new troops to arrive “relatively soon” to bring the U.S. troop presence in Iraq to more than 4,600.

McFarland was expected to be replaced in Iraq in August or September by Army Lt. Gen. Stephen J. Townsend, a veteran of the counter-insurgency wars in Iraq and Afghanistan who now serves as commander of the XVIII Airborne Corps based in Fort Bragg, North Carolina.

Carter did not mention the Apaches or the HIMARS systems in his Baghdad remarks but noted that in addition to the 560 U.S. troops at al-Qayyarah “we’ll bring unique capabilities to the campaign and provide critical support to Iraqi forces at a key moment in the fight.”

The move against Mosul was also likely to involve added risk for U.S. troops. Carter has already approved assigning U.S. trainers and advisors to move forward with the ISF at the battalion level, although Pentagon officials said last week that none of the trainers and advisors had yet worked at the battalion level with the Iraqis.

That was expected to change for the Mosul offensive, which will require the expertise of U.S. troops on the ground, particularly for the bridging operations that will be needed to gain access to Mosul.

Carter began his remarks in Baghdad with condolences for the hundreds of Iraqi civilians killed in terror attacks by ISIS in Baghdad and areas north of the capital, including more than 200 last week in Baghdad’s Karrada shopping district.

The U.S. already shares intelligence with the Iraqis on terror threats, but Carter said he was directing the the Joint Improvised-Threat Defeat Agency — which leads the Defense Department’s efforts to counter improvised explosive device — to provide additional assistance that could enhance security in Baghdad.

Carter’s move to increase the U.S. troop presence left open the question of how it would be funded, according to Sen. John McCain, chairman of the Senate Armed Services Committee.

In a statement, McCain said “While I welcome the President’s decision to send additional U.S. troops to Iraq to support the fight against (ISIS), the President’s defense budget does not take into account this new requirement.”

“The same is true of the President’s decision to retain 8,400 U.S. forces in Afghanistan into next year. These operations will not pay for themselves,” said McCain, an Arizona Republican.