As we discussed in chapter 3, ‘security contacts’ were the fourth major type of contact experienced by 1ATF. They were fought mostly in defence of day and night patrol harbour positions, night defensive positions and fixed defences such as the Horseshoe feature north of Dat Do (see map 2) and fire support bases. In these contacts, the Task Force had selected and prepared the ground.

In keeping with their tactical doctrine, 1ATF patrols sought to conceal their presence at all times so that they increased their chances of surprising the enemy. This fundamental practice applied to day and night harbours: temporary static positions in which security depended primarily on concealment rather than elaborate field defences. The methods used were similar to those for patrolling and ambushing: strict silence, camouflage, perimeter tracks cleared for silent movement, sentries posted, claymores deployed, and each machine-gun manned and ready to fire. Bushcraft skills ensured that the route into the harbour position was not obvious and in any case was covered by the fire of one of the patrol's machine-guns. Once in the harbour position, the patrol settled down to a quiet routine, shifting to night routine after standdown. This stealthy approach contrasted with the patrolling, harbouring and other battlefield techniques of some US Army and Marine units.

The enemy sought to find Task Force patrol harbours and night defensive positions, and to probe them for gaps in their defences so that they could be avoided, or attacked if the opportunity presented. But the constantly changing locations of Task Force patrol harbours, and the risk of ambush, made the task difficult and potentially dangerous. But, if harbours could be located, the enemy was often ready to fire RPGs and automatic weapons into the general area of a patrol harbour rather than launch a full-scale assault. These attacks by fire could cause casualties or encourage the Task Force patrol to return fire, thereby disclosing the full extent of its position. But to achieve even this modest level of attack required the enemy to penetrate unseen past the sentries placed by patrols to detect just such enemy actions. Approaching the perimeter of a Task Force harbour to a distance where aimed fire might be possible was a dangerous task in itself and one in which the enemy was often intercepted.