On 20 September, a force of four Royalist companies of regulars and three of guerrillas launched Operation Diamond Arrow from Salavane, north of Thateng.

[5][3] The town fell to the PAVN, but the Royalist Bataillon Volontaires 46 (Volunteer Battalion 46) hung on in an adjacent stronghold despite casualties of about 40 killed, 100 wounded, and 30 missing.

[3] While the Royalists sheltered within the French-built fort, the communists blasted away land mines and defensive barbed wire to clear paths for frontal assaults by their infantry.

Nail FACs from Nakhon Phanom Royal Thai Air Force Base flew night reconnaissance.

[3] With the besieged Royalists unwilling or unable to appear outside walls to repair the perimeter defenses destroyed in the human wave attack, the barbed wire was replenished via air sowing from C-123s.

[6][3] However, by 5 February, the PAVN had infiltrated the ruined town; they set up an 82mm mortar in a hut, firing shells out through the thatch roof.

The following day, more mines were dropped by F-4 Phantom IIs in a horseshoe bend around the Royalists, limiting the battlefield to a single avenue of attack or retreat.

[6] On 11 February 1970, MR 4's premier unit, Bataillon Infanterie 7 (Infantry Battalion 7), was helicoptered into a mountaintop position three kilometers southwest of Thatheng.

[6] With a gunship flying nightly cover guarding against renewed communist attacks, BV 46 hung onto the Thateng intersection until 4 April.

BI 7 clung to its nearby hilltop position for almost another month before abandoning the battlefield and walking back to its base at Pakse.