Local and state agencies joined 600 soldiers Sunday in the third day of a search for Sgt. Lawrence G. Sprader, Col. Diane Battaglia said.
The 24-year-old was last heard from Friday evening, about an hour before he was supposed to have completed a six-hour solo navigational mission. He was on foot.
"We think he got disoriented on the course and got misdirected," Battaglia said. "In his last message, he said he reached a hard, paved road, and was instructed to call in if that happened. He wasn't able to give any terms of reference as to where he was located."
Military Black Hawks and a Texas Department of Public Safety helicopter scoured the area Sunday, and the Texas Department of Criminal Justice provided bloodhounds, Battaglia said.
"The longer he goes without being resupplied with water or food, or if he is completely lost and disoriented, there would be fear for his physical well-being," she said.
Temperatures reached the low 90s on Sunday and were forecast to do so again on Monday.
The orientation course is set in a remote and rugged area of Fort Hood south of the Fort Hood-Killeen Regional Airport. The area includes hills, fields, dirt trails and woods. Searchers believe Sprader may be obscured by foliage in a wooded area, Battaglia said.
Sprader, who is assigned to the Army's Noncommissioned Officer Academy, was carrying two canteens and a water backpack, she said.
"We do believe he is somewhere on the installation, and that area abuts up next to several public roads," Battaglia said. "We believe he may not be right mentally or physically."