Why were Navy SEALs on front line in ISIS fight?

BAGHDAD -- New video has emerged of the intense battle in Iraq that left a Navy SEAL dead on Tuesday. His team was called in when ISIS attacked U.S. allies and their American advisers north of Mosul.

Only twenty minutes into the battle, U.S. forces knew they were in trouble and they called for back-up. Then things got worse.

The Navy SEAL rescue team found themselves pinned down in an intense firefight with over 120 ISIS militants. Kurdish soldiers and their U.S. advisers were forced to take cover.

The attack seemed to come from nowhere, and Petty Officer 1st Class Charles Keating IV was among those shot in the gun battle.

Even the Blackhawk helicopters that were called in to evacuate Keating came under fire.

ISIS launched the surprise attack at around 7:30 in the morning, near the village of Tel Asqof.

According to U.S. officials, the militants flooded in from the south, piercing the front line with three suicide truck bombs and bulldozers.

The Americans fought for nearly two hours before finally getting away. U.S. officials told CBS News the area had been relatively quiet for a month, and was considered low-risk.

It shows that the front line against ISIS can change in a flash, and U.S. forces are right up close to it.

But U.S. military officials there stressed that those SEALs were only brought in to back up Americans, and would not have joined the firefight otherwise.