Dien Bien Phu;
Also, as Jester has said, De Castres didn't think the Viet Minh could bring up heavy artillery, and the entire site was based around this premise.
However, at an unknown human cost, Giap
man packed soviet 122mm howitzers through the forest to bombard the base. The French 105mm howitzers, a good gun but designed to be the upper limit of air-mobility, couldn't answer to the range or weight of shell and the Viet Minh counter-battery fire destroyed the base.
De Castres and the French command made several major mistakes that PCs could use to reduce other firebases, I'll summarise everyone's points here for a list;
- Inability of supply
- Vantage points outside the reach of the base's weapons
- Under estimation of the enemy
- Base too large to defend
- Base that once the perimeter is penetrated has no fall back line
- Lack of aggressive patrolling
- Lack of a rapid reaction force
- Inability to move reserves across base to recapture strong points
Of course, making these things happen is better than just hoping they're there. Giap constrained movement with his guns. Supply can be cut of and attacks made on siege caches. The opponent can be invited to underestimate the threat and to expand to deny points that thins his troops.
Vietnam really suffered due to the armoured enclave mentality. It is estimated that 80% of the troops in theatre were need to man and secure the bases, leaving very little for combat tasks. This underlies the absolute necessity in securing the zone so troops can move about.
This is the real fight I see occurring in T2k. If an area has insufficient troops to man a continuous trench line, and many places will (I see trenches mainly happening on the Oder and Rhine lines in a v1 campaign) there will be isolated strong points surrounded by an artillery zone. In the no-man's land between artillery zones the troops fight each other, trying to secure choke points, attack movement and deny resources.
Attacks on cantons will be spoiling in nature. Crops can be attacked with chemical weapons which damage the ground and make the food inedible. Patrols will be ambushed and then the attackers withdraw before the base fire can be directed onto them. Harassing fire from mobile weapons such as mortars, SPGs and technicals can be directed onto bases and then moved before retaliation to keep base defenders on edge and tired. Some of these attacks may be sufficient to get some cantons to just move somewhere quieter.