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Defile Operations at the NTC

by LTC Michael Shields, Brigade S3 Trainer, NTC

(This is the second of two articles by LTC Shields on the difficulties light task forces (TFs) experience when conducting truck infiltration missions at the National Training Center (NTC). His first article, published in CALL's CTC Quarterly Bulletin, 3d Qtr, FY 99, No. 99-14, Oct 99, "Truck Infiltration (Assault) Planning in a Heavy/Light Scenario," presents tactics, techniques and procedures (TTP) for planning and executing such a mission. This second article goes hand in hand with the first. It discusses one of the drills that is often a major factor in determining the success or failure of a unit's infiltration mission at the NTC - defile operations.)

ISSUE: Light task forces (TFs) are challenged when planning for, and executing, defile operations.


1. Figure 1 and Figure 2 illustrate a common scenario observed at the NTC when TFs attempt to conduct a defile drill.

Note that the TF began entering the defile at approximately 0430 (limited visibility because of darkness). At approximately 0721 (daylight), the TF ordered the company/team (CO/TM) to pull back. Four plus hours were consumed trying to get through the defile. The CO/TM was rendered combat ineffective.

2. Given the restricted terrain at the NTC, it is inevitable that infantry task forces (sometimes armor) conduct defile operations. Defile drills are combined arms operations whether conducted at company or battalion level. Defile clearing operations are conducted in three phases (reference FM 71-1, Tank and Mechanized Infantry Company Team):

a. The approach phase focuses on moving combat power into restricted terrain and positioning forces to begin clearing operations.

b. The clearing phase begins as the infantry assaults through the restricted terrain. The infantry must clear both sides of the defile and along the ridgelines and walls of the defile.

c. The securing phase begins when the defile has been cleared. The TF must secure the far side of the defile beyond the restricted terrain. Securing the far side often includes continuing the attack to destroy enemy forces covering the exit of the defile and establishing support-by-fire (SBF) positions on the far side to protect follow-on forces assuming the fight.

3. This article addresses planning considerations by phase and the graphics show "a way" to help visualize the narrative. The task organization depicted in the scenario is an example and not prescriptive in nature. Ideally, reconnaissance forces identify a bypass so the TF is not required to clear enemy-occupied restricted terrain. This article focuses on the worst-case scenario, where a TF has to fight through a defile.


1. Approach Phase.

a. Critical to success in the defile is positioning reconnaissance forces throughout the restricted terrain to identify the composition, disposition, and strength of enemy forces including obstacles. Consider the use of terrain products (such as Terra Base) to assist in visualizing the defile.

b. Once on the far side, reconnaissance forces establish surveillance positions or observation posts (OPs) to observe enemy counterattack avenues of approach.

(1) These reconnaissance forces are generally not the TF scouts. TF scouts typically conduct reconnaissance missions vicinity of the TF objective. The reconnaissance assets must be pulled from within the TF. Possible assets include infantry (such as squads/teams), forward observer (FO) teams, or engineer reconnaissance teams (ERTs).

(2) Stinger teams should be considered in the reconnaissance plan if the air threat dictates.

(3) The TF mortars should be positioned to provide fire support to the reconnaissance forces.

c. Infantry squads conduct a reconnaissance on both sides of the defile (see Figure 3). A squad from Team B (TF advanced guard) reconnoiters (recons) the north side of the defile, and a rifle squad from A Company recons the south side of the defile. ERTs conduct a route reconnaissance of both passes. The ERT in the south does not continue beyond the tank ditch. The obstacle in the north is identified as a surface-laid mine/wire obstacle and can be breached with TF assets.

d. The TF commander elects to attack through the northern pass. Critical friendly zones (CFZs) are activated covering the northern pass and the TF main body. No fire areas (NFAs) cover reconnaissance assets. The TF mortars position to cover the reconnaissance forces and have sensor zone coverage. The sensor zone is a force protection measure to protect the TF mortars when firing from within the CFZ. Reconnaissance assets conduct long-range surveillance and observation of enemy counterattack routes, and the engineers maintain surveillance of the obstacles.

e. The TF then positions forces to prepare for clearing operations. Truck-mounted and mechanized infantry move forward to dismount points while the advanced guard (initial TF maneuvering element (ME)) overwatches their move. The role of the advanced guard is to destroy enemy forces overwatching the entrance to the defile and to fix enemy forces trying to reposition or reinforce (isolate the defile) (also consider integration of attack aviation). Mortars, air defense, and combat service support assets move into position.

f. The TF is operating two tactical command posts with the S3 moving with the advanced guard and the battalion commander with the main body (or some variation). The TF commander must position his command and control facilities to maintain situational awareness and control fire and maneuver.

g. The main body remains back, out of direct fire and observation by enemy forces securing the defile. Direct fire control measures (terrain or threat-based) are established to prevent the fratricide of friendly forces as they approach the defile and begin clearing operations, and NFAs are established to protect reconnaissance forces on the far side of the defile. The TF should consider and apply surface danger zones (SDZs) and minimum safe distances (MSDs) for indirect fires when developing the fire plan. (Clearance of fires and direct fire control are extremely difficult when conducting defile operations. A good litmus test is to ask yourself if you would execute your plan in a live-fire exercise).

h. Reconnaissance forces continue to conduct surveillance, ensuring they move out of SDZs/MSD areas of the TF (see Figure 4).

i. The TF begins positioning forces to set the conditions for the clearing phase.

(1) Team B (-) occupies support-by-fire (SBF) position B1 and orients fires between target reference points (TRPs) 1 and 2, to destroy enemy forces on OBJ Cat, to prevent the enemy from placing effective direct fires on the infantry forces as they move forward to dismount and occupy assault positions. TM B's infantrymen are consolidated at company level to clear the north side of the defile.

(2) One mechanized platoon (minus infantry) occupies SBF B1A in the south, orienting fires between TRPs 2 and 3, to destroy counterattacking enemy forces, to protect the southern flank of the TF.

(3) A Company, mounted on 5-ton trucks, moves forward to a dismount point to clear the south side of the defile.

(4) The ERTs move back to link up with the engineer platoon (out of SDZs/MSDs).

(5) The artillery battery is firing WP to obscure the TFs movement to the dismount point and assault positions.

(6) The mortar platoon is suppressing enemy positions. The focus of fires is on OBJ Cat.

(7) The remainder of the TF (on trucks) is in a security halt, dispersed, and out of direct fire range of the enemy. The TF is covered by an active CFZ.

j. The approach phase ends when the infantry (clearing force) is prepared to conduct the assault through the defile. The TF plans and executes suppression and/or obscuration fires (S.O.S.R.) during the approach phase to help set conditions for the clearing phase.

2. Clearing Phase.

a. The clearing phase begins as the infantry assaults through the restricted terrain. The Vee formation (not the "school solution") is uniquely suited for defile operations at TF level; however, companies may move using some other formation, such as echelon or wedge, based on the enemy situation. The Vee formation facilitates clearing north and south of the defile with heavy forces supporting along the mounted avenue of approach.

b. The infantry should clear from the top down and orient on an objective(s). The TF scheme of maneuver must prevent simultaneous clearing by two companies abreast because of the high risk of fratricide as they both clear from the top down and shoot back at each other. The TF should bound companies forward (in the Vee) and develop a scheme of fires (including direct) to shift/lift fires as units approach SDZs (consider the use of restrictive fire lines (RFLs) and TRPs) and MSDs. Use phase lines as minimum safe lines to prevent movement within a SDZ or MSD for indirect fire.

c. Heavy force employment considerations include the following:

(1) Bradley Fighting Vehicles (BFVs) can elevate the 25mm main gun higher than the M1 tank's 120mm main gun (+60 degrees versus +20 degrees for the tank).

(2) Armor-piercing, fin-stabilizing, discarding SABOT (APFSDS) rounds from the 25mm are less restrictive than the 120mm SABOT petals.

(3) The M1 tank can be used to accomplish specific missions within its capabilities such as destroying armor, bunkers, and fortifications. Use of tanks or Bradleys should be situation dependent.

(4) Consider employing the Javelin, TOW, and AT-4 to destroy fighting positions/bunkers.

(5) Engineers should move with the infantry to provide a manual breaching capability. This allows the infantry to focus on the enemy threat. Heavy engineers with the CO/TM should be augmented with mobility assets, such as an AVLM, ACE, or a tank with plow if a mechanical breach requirement is identified during the planning process. The TF may have to ask the brigade combat team (BCT) for additional assets. The M1 tank plow can clear a four-meter width to provide a limited sub-surface and surface minefield clearing capability (18" spoil requirement IAW NTC ROE).

d. The clearing phase ends when the defile has been cleared to the far side. Figures 5A, B, C and D depict "a way" to work through the fire control challenges of a defile drill. As the figures illustrating the clearing phase progress, previously used graphics no longer pertinent are deleted to aid in clarity.

(1) The TF has designated two march objectives to facilitate controlling maneuver and fires. The defile is subdivided it into OBJs Cat and Dog. OBJs Cat and Dog are split by RFL 1, which runs down the main road. Each OBJ is further subdivided into OBJs North and South.

(2) The TF designates terrain-based fire control measures to control direct fires. Additional fire control measures have been established and are discussed in the clearing phase.

e. Figure 5A. For the purpose of this article, B Company refers to infantry from Team B. Both infantry companies are in assault positions vicinity PL Birch, the final coordinating line. As B Company prepares to cross PL Birch, indirect fires lift off OBJ Cat North and shift to OBJ Cat South (the focus of fires) and OBJ Dog North. B Company crossing PL Birch (FCL) is the trigger for Team B and A Company to shift all direct fires south of the RFL 1 (vicinity TRP 2-OBJ Cat South). Both companies are weapons tight. A Company remains in an assault position short of PL Birch until OBJ Cat North has been cleared. Once B Company has cleared OBJ Cat North, they occupy SBF B2 and orient fires on TRP 2 (OBJ Cat South). Team B (-) lifts fires off of OBJ Cat (weapons hold). A Company (the TF main effort) crosses PL Birch (RFL 2 in effect for the BFV platoon in the south) and assaults to clear OBJ Cat South (from east to west). The focus of indirect fires shifts to OBJ Dog North. B Company (weapons tight) shifts fires in support of A Company's assault based on procedural control measures. With RFL 1 in effect, B Company cannot engage OBJ Cat South without coordination with A Company and the TF (establishing HQ). B Company prepares to continue the attack to OBJ Dog North.

f. Figure 5B. Once OBJ Cat South is clear, A Company occupies SBF A1 and orients fires on TRP 5 (OBJ Dog South). B Company begins movement toward PL Maple and the engineers conduct a manual (or mechanical) breach and create a lane through the obstacle. Once the lane is clear, a BFV platoon from Team B (-) moves forward through the obstacle. The BFV platoon moves to the front line trace of the infantry companies and occupies SBF B3. The BFV platoon orients fires on TRP 5 (RFL 1 in effect) with a task to destroy enemy armor in the pass then suppress infantry on OBJ Dog South (weapons tight). The BFV platoon and A Company can engage enemy north of RFL 1 with coordination. The intent is to isolate OBJ Dog North from Dog South with direct fire with the focus of indirect fires remaining on OBJ Dog North until B Company crosses PL Maple (FCL). No change to the TF disposition.

g. Figure 5C. Once B Company crosses PL Maple (FCL), indirect fires shift off OBJ Dog North with the focus of indirect fires on OBJ Dog South. A Company and the BFV platoon (weapons tight) remain focused on TRP 5 (RFL 1 in effect). Once OBJ Dog North has been cleared, B Company (weapons tight) occupies SBF B4 and orients fires south on TRP5 (OBJ Dog South). A Company begins movement to PL Maple. The TF (-) mounted elements transition to REDCON 1.

h. Figure 5D. A Company crosses PL Maple which is the trigger for the BFV platoon to lift fires from OBJ Dog (weapons hold), B Company to lift or shift fires to the west (weapons tight), and the focus of indirect fires to shift to enemy CATK avenues of approach. A Company clears OBJ Dog South (with RFL 1 in effect) and then occupies SBF A2, orienting fires to the west (weapons tight). The BFV platoon moves abreast of A and B Companies and occupies SBF B4 to overwatch the movement of Team B (-) through the defile. Team B, the TF advanced guard, initiates movement through the defile. The 2d serial behind the advanced guard initiates movement toward PL Birch. The TF is transitioning to the securing phase.

Note. Because of limited CL V and the higher probability of fratricide during the defile operation, weapons free is not authorized. Subordinate commanders may issue more restrictive fire control measures based on their situation with regards to weapons safety posture (see FM 71-1).

3. Securing Phase.

a. The TF should secure an area large enough to accommodate the TF as it exits the defile. The reconnaissance forces and clearing forces can provide terrain and enemy information to aid in securing the defile. The TF cannot allow itself to get "bottlenecked" in the restricted terrain. The TF must be able to defeat counterattacks during passage. Once through, the TF should rapidly gain control of the tactical movement (approach march) and continue the attack. The TF may have to consolidate and reorganize, to include conducting casualty evacuation (CASEVAC), vehicle recovery, and CL III/V resupply (for example, CLIII for M1 tanks), prior to continuing the attack. The TF zone of attack may include additional restricted terrain and another defile drill.

b. Figure 6. The BFV platoon moves forward in zone to begin clearing an area large enough to accommodate the advanced guard.

(1) Reconnaissance forces link up with clearing forces and establish security on the far side of the defile.

(2) The engineers clear, expand, and mark the route through the pass.

(3) Team B links up with its southern platoon and initiates movement through the pass.

(4) A TOW platoon replaces the mechanized platoon in the south and provides flank security.

(5) The infantrymen on the north side of the pass initiate movement to link up with the Bradleys.

(6) The mortar platoon is fighting split section with a section moving behind the advanced guard to set up on the far side of the pass. One mortar section remains set to provide fire support during movement through the pass.

(7) The main body has started to move forward by serial/phase line to facilitate rapid movement through the defile. METT-T determines the priority for moving through the defile. Consider the use of military police to control movement (battlefield circulation).

c. Figure 7. The advanced guard (weapons tight) has secured an area large enough to accommodate the entire TF on the far side of the defile. The TF main body has begun movement through the defile, one truck-mounted rifle company (serial) at a time. The infantrymen on the south side of the pass have initiated movement to link up with their trucks. D Company (or AT platoon) provides flank security during movement.

Note. Although not graphically depicted throughout the scenario of this article, CSS assets must be positioned to support the defile operation.


The intent of this article is to highlight key planning considerations for the execution of defile operations. Defile drills are combined arms operations. If not planned, rehearsed, and executed properly, defile operations can result in significant combat power losses, a loss of momentum, and the TF reaching its culminating point before it achieves its task and purpose. Execution of a defile drill is a critical event. It is a means to get to the end (accomplishment of the TF task and purpose). Also refer to "Truck Infiltration (Assault) Planning in a Heavy/Light Scenario," CALL's CTC Quarterly Bulletin, 3d Qtr, FY 99, No. 99-14, Oct 99.

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