for Phase I were to conduct air and ground assaults to block enemy escape routes in the northern and eastern portion of the area of operations; conduct search and destroy operations; secure lines of communication from Tay Ninh to Katum (consisting of approximately forty-five kilometers of Route 4); and provide security during engineer construction at Katum and Prek Klok. On D-day the 1st Brigade (Colonel Caldwell), comprised of four infantry battalions and Task Force WALLACE was to assault by air and establish blocking positions in the northern portion of the area. The 173d Airborne Brigade (Brigadier General John R. Deane, Jr.) with three battalions was directed to assault by air on D-day and establish blocking positions from Katum to the 1st Brigade area; this put the 173d on the northeast portion of the horseshoe. Respon-sibility for the eastern leg of the horseshoe was assigned to the division's 3d Brigade (Colonel Marks). His brigade included one mechanized battalion, an infantry battalion, and the cavalry squadron with one tank company attached. This brigade was to attack north on D-day along Route 4, establish fire support bases, and link up with the 173d. Each of the brigades had at least one artillery battalion in direct support.
During Phase I of Operation JUNCTION CITY the 25th (Tropic Lightning) Division under General Weyand employed its organic 2d Brigade with other units under division control, namely, the 3d Brigade, 4th Infantry Division; 196th Light Infantry Brigade; 11th Armored Cavalry Regiment (-); and two South Vietnamese units, the 1st and 5th Marine Battalions (Task Force ALPHA). The 1st Brigade, 9th Infantry Division, part of the division's task organization, was placed under the operational control of the 1st Infantry Division later in Phase I.
Under the 25th Division's plan, the 3d Brigade, 4th Infantry Division (Colonel Garth), would block and continue to conduct search and destroy operations from the area which it held at the close of Operation GARDEN on 21 February in the far western portion of the operational area. Assigned to the brigade were one mechanized infantry battalion, two infantry battalions, one troop of cavalry, and a company of armor. Operating closely with Garth's brigade was the 196th Brigade (General Knowles), which on D-day would conduct airmobile assaults with its three infantry battalions along the northwest portion of the horseshoe to establish blocking positions and seal enemy escape routes into Cambodia. The positions of the 25th Division units would thus form the broad left leg of the horseshoe and would complete, along with the 1st Division, the seal of the operational area. The division's 2d Brigade (Colonel Marvin D. Fuller) and Colonel William W. Cobb's 11th Armored