Contingency Operating Site (COS) Kalsu, formerly known as Forward Operating Base (FOB) Kalsu and also referred to as Camp Kalsu, was a U.S. military installation located in the Babil province of Iraq, specifically in Iskandariya, a city about 20 miles south of Baghdad. It was named after Bob Kalsu, an NFL player for the Buffalo Bills and an Army lieutenant who was the only active professional football player to be killed in Vietnam.

COS Kalsu was strategically situated in the region colloquially referred to as the “Triangle of Death” because of the high level of insurgent activity. As such, it played a vital role in operations in this region, serving as a hub for U.S. and coalition forces to conduct and respond to developments effectively.

Over the years of its operation, several different units were stationed at COS Kalsu. These included elements of the 2nd Brigade, 10th Mountain Division, the 2nd Brigade, 3rd Infantry Division, and the 172nd Infantry Brigade. These units carried out a wide range of operations, including counterinsurgency missions, patrols, and training of local Iraqi forces, contributing to the broader mission of stabilizing the region.

The facilities at COS Kalsu were designed to support the troops stationed there, maintaining their operational readiness and morale during their deployment. These included housing and dining for personnel, operation centers, training areas, and logistical support.