Washington (CNN) -- A U.S. Army officer who was honored for valor after his combat outpost in Afghanistan was attacked has also received a letter of reprimand for failing to secure the base before the attack, according to Army officials. Such a letter normally would prevent career advancement.

U.S. Army Capt. Matthew Myer received the Silver Star for his part in repelling a Taliban attack on his small combat outpost in eastern Afghanistan in July 2008.

The attack, near the village of Wanat, is still the deadliest ground combat of the war involving U.S. troops. A coordinated Taliban attack from the steep hills surrounding the base almost resulted in the outpost being overrun.

According to troops who survived, the Taliban came at the base with about 200 fighters, outnumbering the U.S. forces at the base. In the end nine soldiers were killed and 12 were wounded. About 100 Taliban were killed.

Despite the heavy U.S. death toll, Myer was awarded the Silver Star for calling in aircraft to beat back the fighters, some of whom had breached the base walls, according to U.S. military officials in Afghanistan.

After the attack, the U.S. military scrutinized how enemy forces were allowed to get as close to the base as they did. Officials familiar with the after-action review said Taliban fighters got within grenade-throwing distance of U.S. troops.

Myer even called in close air support to hit enemy targets just 10 meters from his own position, according to officials familiar with the after-action report.

Four-star Gen. Charles C. Campbell was chosen to review the final investigation and make disciplinary decisions. Campbell decided Myer would receive a career-ending letter of reprimand for failing to prepare the base's defenses sufficiently against an enemy attack. Myer was informed this week of his punishment, according to U.S. military officials. CBS News first reported his punishment.

Two of Myer's senior commanders, who were not at the base during the attack, also received similar career-ending letters of reprimand. Officials would not elaborate on the reasons for the reprimands.

Army officials acknowledge the base, built to protect the people in Wanat, was at the bottom of a valley surrounded by high hills, an almost impossible location to defend.

According to one U.S. military official familiar with the general's decision to reprimand Myer, "He saw the evidence and made a decision based on that." However, the same official said, "Unless you've been there, you don't know how hard those places are to defend."

Myer and his two senior officers are allowed to appeal the punishment.

Another U.S. military official familiar with the review said he expects the three officers to meet with Campbell to plead their cases.