(CNN) -- The nation's oldest Army armor unit at Fort Carson in Colorado remained in lockdown for a second day Friday, after the post began investigating "the unauthorized removal of government property," the military said.

The lockdown applies to the 1st Battalion 66th Armor Regiment "Iron Knights," an Army spokesman said.

"The 66th Armor Regiment is the oldest Armor unit in the United States Army, tracing it's lineage to the beginning of the Tank Service in February 1918," its Facebook page says.

Fort Carson chief of media Dani Johnson declined to elaborate Friday on the type of property allegedly removed.

"This type of lockdown is a unit lockdown, which is at a commander's discretion," Johnson said.

Between 500 to 750 soldiers are affected "at most" at the 26,000-soldier installation near Colorado Springs, Johnson said.

"So you're talking about a very small impact," Johnson said.

This type of lockdown is not common, a spokesman said.

The measure means that soldiers remain on-duty working on the base instead of being allowed to go home, CNN affiliate KKTV reported.

The property purportedly missing was from that unit, and base authorities searched outgoing vehicles Thursday to make sure property was not being removed from the base, the affiliate reported.