How the US Is Helping the Mosul Offensive

— -- The fight to retake Mosul from ISIS involves 28,000 Iraqi and Kurdish military forces, but American advisors and aircraft are also playing a vital role in the operation.

According to U.S. officials, more than 100 U.S. military advisors are accompanying Iraqi special operations and Kurdish military forces involved in the Mosul offensive.

What they are doing is no different from what U.S. advisors have done over the last two years in Iraq in advising and assisting Iraqi and Kurdish military leaders with their battlefield planning and operations.

A larger number of the almost 5,000 American troops in Iraq are providing logistical, intelligence and enabling support for the Iraqi offensive.

ABC News takes a look at how American military forces are helping in the Iraqi military offensive against ISIS in Mosul:

Is the U.S. military on the front lines of the Mosul offensive

The U.S. military mission in Iraq has two goals, to train the Iraqi military to fight ISIS and to then advise and assist those forces on the battlefield.

Only a few hundred of the 4,880 U.S. military personnel in Iraq are advisors working alongside Iraqi military leaders to assist them in their battlefield operations. Many of the rest are involved in providing logistical and enabling support for the Iraqi military.

All 12 of the Iraqi and Kurdish brigades involved in the Mosul offensive have been trained by the United States and its coalition partners, a process that took much of the past two years.

The advisors working with the Iraqi Army are assigned to the division headquarters level located well back from the front lines. It is unclear how many American advisors may be working with the Iraqi Army divisions playing a part in the Mosul offensive.

Advisors accompanying the elite Iraqi Counterterrorism Service and the Kurdish Peshmerga also serve at the headquarters level and are not supposed to be on the front lines. But given the reality of how those units operate on the battlefield this means the American advisors are closer to a combat environment. According to U.S. officials, there are more than 100 military advisors working alongside Iraq's elite Counterterrorism Service (CTS) and Kurdish Peshmerga as part of the Mosul offensive.

The advisors working with these units work in small teams accompanying their larger Iraqi and Kurdish units.

The advisors play a key function by serving as forward air controllers pass along targeting information from the Iraqis and Kurds to military planners coordinating airstrikes. They can do this either from a battlefield setting or at the division headquarters level.

How else are U.S. forces supporting the Mosul offensive?

Well behind the front lines American troop are also contributing to the Mosul offensive with logistical support, artillery firepower and airstrikes.

There are several hundred American troops operating at the airfield known as Qayyarah West on the western bank of the Tigris River. Since it was seized from ISIS in September the base has become the major logistical hub for the Iraqi Army's push northward to Mosul on the main south to north highway that leads to Baghdad.

American personnel have been busy fixing the airstrip to enable the quick turnaround of supplies the Iraqi Army will need to sustain itself for what promises to be a lengthy battle.

They are also there to assist their Iraqi counterparts in maintaining and supplying the Iraqi military's largest operation against ISIS.

American troops are also at a base on the eastern side of the Tigris River in Makhmour. They first arrived earlier this year to provide artillery support to Iraqi forces at the base and have helped with offensive Iraqi operations since then.

One of the artillery systems being used to help the offensive is the HIMARS rocket system that can strike targets deep in ISIS territory.

Up above, American and coalition aircraft are providing Iraqi troops with airstrikes to help their offensive. Since October 1 the coalition has carried out more than 70 airstrikes in and around Mosul in preparation for the offensive. Those airstrikes will continue as the Mosul offensive continues.