Pentagon efforts to train and arm Kurdish fighters in the ongoing fight against the Islamic State in Iraq have been helpful, but more needs to be done, according to a new assessment from the Defense Department's inspector general.

The IG report released last week found serious problems in the distribution and sustainment of American gear and the lack of formal training in the region, based on extensive field research conducted between October 2015 and December 2016.

The Kurdish fighters — known as peshmerga — proved stalwart defenders of Iraqi territory as ISIS blitzed through the country in the summer of 2014, when other Iraqi security forces buckled and disintegrated.

Since the U.S. engaged in the fight with the stand-up of Operation Inherent Resolve in October 2014, the peshmerga have been a critical ally in slowly rolling back the terrorist group with the support of U.S. airstrikes.

While the report validated U.S. efforts to build peshmerga capacity thus far, they have fallen short in several key missions.

One issue the IG noted was the failure to deliver U.S. equipment purchased for the Kurdish Security Forces.

The $1.6 billion Iraq Train and Equip Fund established in late 2014 allowed the purchase of enough equipment to arm 4,000 peshmerga, or two light infantry brigades, including personal protective equipment, weaponry, vehicles and communications gear.

"At the time of our fieldwork, the U.S. had not delivered the majority of the brigade set equipment to the KSF," the study found.

Equipment donated from coalition forces, however, fared much better.

Central Command is responsible for both publishing Kurdish gear requests and, once equipment is donated from other nations, running the distribution pipeline from Baghdad to Kurdistan to peshmerga commanders in the field.

"Our observations while conducting fieldwork confirmed the availability of Coalition-donated equipment that enhanced peshmerga capabilities during their operations against [ISIS]," the researchers found.

But CENTCOM lacks visibility on this distribution and a plan to sustain the equipment.

Not having a streamlined process means an increased risk both of duplicate deliveries and a loss of accountability, according to the study.

"Additionally, not knowing delivery dates of equipment hampered the ability of logistics advisors to provide guidance to enable the Ministry of Peshmerga to adequately plan for deliveries and subsequent distribution," the report states.

Direct U.S. military training and advising of Iraqi security forces has been a key pillar of the U.S. strategy to fight ISIS.

The emphasis was put on bolstering the rest of the Iraqi military, though, and training the Kurds was primarily left to other coalition forces.

In January 2015, the Kurdish Training Coordination Center was established in Erbil and staffed by eight European militaries.

Four training sites were set up throughout Kurdistan, and peshmerga began running through 23-day training courses covering weapons training, small-unit maneuvers and staff training.

The KTCC doesn't fall under U.S. command, but American liaison and special forces took the initiative to provide critical training on an informal basis.

Drawing on long-established relationships with Kurdish leadership, they've also taken on advising and assisting the peshmerga through offensive operations, surveillance and reconnaissance, communications and explosive ordnance disposal.

But it is unclear how sustainable the informal mission is, and the IG urged Combined Joint Task Force – Operation Inherent Resolve to "formalize and continue the current advise and assist missions being conducted in training development, logistics and resource management."

What is clear is that the peshmerga has become a professional force to be reckoned with.

Since absorbing the initial shock of the ISIS invasion, they've steadily rolled back the terrorist group, most notably the liberation of Mount Sinjar in November 2015 to sever ISIS supply lines to and from Mosul.

Now Iraqi forces are engaged to liberate that city after two years of draconian ISIS occupation, and the peshmerga have an active role.

"With U.S. and Coalition-tailored train, advise, and assist efforts, and equipping support, the KSF has demonstrated the capacity to defend Iraqi Kurdistan against [ISIS] incursions, and to liberate key territory and towns important to counter-[ISIS] operations," the IG report concludes.