He is ordered to reoccupy a nearby deserted hamlet named Muc Wa on the Da Nang-to-Phnom Penh highway - which a decade before had been the scene of a massacre of French soldiers during the First Indochina War.

Burnt-out Command Sergeant Major Oleozewski served with Barker in Korea, and has already done three tours in Vietnam (his last assignment saw his previous unit massacred).

Maj. Barker sends the new men plus Corporal Ackley, a communications expert, to garrison Muc Wa with a half-French, half-Vietnamese interpreter/interrogation specialist named Nguyen "Cowboy".

A hardcore squad of Hmong mercenaries and a motley mob of about 20 South Vietnamese Popular Force civilian "troops", equipped with various firearms.

After the group encounter a booby-trapped roadblock on the way to Muc Wa, they capture a lone Viet Cong soldier who is beheaded by Cowboy when the man refuses to divulge information.

Courcey leads a patrol that finds Vietnamese women and children fishing along a small creek despite intelligence saying no civilians live in the area.

The next morning, Barker travels to Saigon to meet Colonel Minh, the region's military leader, to request he send at least 300 ARVN troops to Muc Wa.

Minh refuses, claiming he needs the troops in Saigon to prevent a potential coup, but he offers the reinforcements in exchange for 1,500 artillery shells.

After ignoring Oleonozski's warnings, Lt. Hamilton is killed trying to rescue a badly wounded man who was left behind by a combat patrol.

The next morning, Harnitz finally orders Barker to withdraw all American troops from Muc Wa, which is now believed to be besieged by the 1,000-strong 507th Viet Cong battalion.

The younger actors cast were Marc Singer as infantry Captain Al Olivetti, a gung-ho career officer seeking to earn the Combat Infantryman Badge, and Craig Wasson as Corporal Courcey, the idealistic college-educated draftee who wants to see what a real war is like.

The screenplay by Wendell Mayes was shopped around for years with various older leading men such as Robert Mitchum, William Holden and Paul Newman offered the role of Major Asa Barker.

At one of its revivals, it was described as: A cult fave – and deservedly so – Go Tell the Spartans was hard-headed and brutally realistic about our dead-end presence in Vietnam; released the same year as Coming Home (United Artists) and The Deer Hunter (EMI Films released by Universal Pictures), the film won critical admiration, but audiences preferred individualised sagas, sentiment, and romantic melodrama.

This is one of Lancaster's best performances: embittered, a cog in the military juggernaut, this good man foresees the killing waste to come.