One of the largest units in the Iowa National Guard has been put on alert for possible federal active duty.The 1st Battalion 168th Infantry unit has about 670 members based in seven Iowa towns — Carroll, Corning, Council Bluffs, Denison, Glenwood, Shenandoah and Iowa City. Guard spokesman Major Greg Hapgood explains the unit’s duties. They’re an infantry battalion that’s air-assault qualified, meaning they can repel from helicopters into virtually any environment, and can be used to close with the enemy, and take and hold key terrain, installations and facilities. Major Hapgood says the alert means Guard members need to prepare for the likelihood they’ll be shipping out soon, perhaps to Iraq or Afghanistan.Hapgood says the mobilization date and duty location have not been determined. The citizen-soldiers may be ordered to active duty for one year, but could be gone for two years. The unit hasn’t been mobilized since World War Two.