APPENDIX B
ENGINEER-PLANNING CALCULATIONS
GENERAL
ENGINEER PLANNING
Preparation time is the time required to improve routes and riverbanks to support the units that will use the site. It also includes the time required to construct rafts and bridges. Rafting-site capacity is the number of raft round trips per hour. The engineer calculates rafting-site capacity by multiplying the number of raft trips per hour by the number of rafts and the number of centerlines at the site (see Table B-1). Centerlines must be at least 100 meters apart. Each assault company needs 200 meters of river frontage. Figure B-1 shows the determination of rafts per hour and the capacity of the assault site for the division crossing overlay. The site overlay provides additional details necessary to ensure that each brigade has sufficient potential crossing sites within its boundaries. Table B-2 provides planning factors for assault-boat operations.
Rules of thumb for making this determination follow:
- A brigade requires 31 assault boats to cross a battalion with three companies in the first wave. With 70 boats, it can cross two battalions at once. Generally, the boats with the corps bridge companies can handle these requirements.
- A brigade requires two bridges or the equivalent bridging configured into rafts.
The engineer planner uses the above rules of thumb to task-organize engineers that are supporting each crossing area. The division engineer then develops a rough crossing time line using pure battalions. This provides sufficient information for division planning, without requiring detailed knowledge of the brigade's plan. Table B-3 provides necessary planning factors (field trains are not included). Figure B-2 illustrates a crossing time line using 6-float rafts.
The brigade headquarters does the majority of planning for the detailed crossing. During the mission analysis, the brigade engineer also develops a crossing time line to provide initial buildup-rate information to the maneuver planners when they outline possible schemes of maneuver. This time line is the same as the time line that is developed at the division and may be provided by the division engineer.
Once the commander identifies the COAs to develop, the staff engineer develops crossing-area overlays for each (see Figure B-3). These overlays are developed by using information from the site overlay, along with additional terrain data. The crossing-area overlays show staging areas, holding areas, call-forward areas, and routes for each crossing site included in the COA. A crossing-area overlay is necessary for each COA. The overlay for the COA eventually selected is later modified by adding ERPs, TCPs, and crossing-area-headquarters information and is used to support the operation.
When maneuver planners develop COAs, they assign crossing sites and the order of crossing to units and task-organize the pure maneuver battalions into TFs. The engineer uses this information to construct a crossing time line for each COA. He calculates the number of vehicles and raft loads for each unit using pure company figures from Table B-4. The company's raft requirements do not include the field trains. The engineer then calculates the crossing time for the unit by using the crossing capacity of the site assigned to it. The crossing time line shows these crossing periods, by site, based on the order of crossing. The engineer then develops a detailed crossing time line based on the task organization (see Figure B-4).
During the comparison of the COAs, the engineer uses time lines, brigade-site overlays, and crossing-area overlays to demonstrate the differences in the crossing plans. After the commander has selected the COA for the mission, the staff converts it into a detailed plan. The engineer develops a vehicle-crossing-capability chart.
He starts by displaying the capabilities of each crossing site in terms of raft loads per hour (rafting operations) or vehicles per hour (bridging operations). Since the crossing rate for rafts is less during darkness, each site shows total raft trips separately (during day and during night). An example of the product of this first step is shown in Figure B-5).
The engineer determines the crossing requirements using the factors from Table B-4. He then blocks out the crossing periods for all units based on site assignment, site capability, and the crossing order in the scheme of maneuver. After adding the units' crossing periods to the chart, he coordinates the plan with the S3 to ensure that the units will arrive on the far shore by the times they are needed (see Figure B-6). If not, the S3 and engineer work together to adjust the crossing order of subordinate units. The basic technical information remains constant as different crossing sequences are checked until one meets far-shore requirements. The vehicle-crossing-capability chart is the primary tool for finalizing the crossing plan.
After the crossing order has been established, the engineer develops the crossing- synchronization matrix (see Figure B-7). This is the tool that the CAC and CAE will use to synchronize the execution of the crossing. It is constructed as a chart, with the unit's locations and activities displayed by time on the upper half and terrain occupation displayed by time on the lower half. The staff can follow each unit's location as the operation progresses and can easily see potential conflicts resulting from changes. The matrix also provides critical information for traffic control.
The crossing synchronization matrix is constructed backwards by first portraying the units' crossing times established from the vehicle-crossing-capability chart, then by using road movement times to show route usage and staging-area times. The time required for the crossing of the assault force is also included. Once all of the units are displayed, the same information is transferred to the lower terrain portion of the matrix. The staff immediately resolves any conflicts they discover while preparing the matrix.
The final engineer planning step is developing the engineer execution matrix (see Figure B-8). It displays subordinate units' task assignments by time. It is useful both for tracking unit execution and for aiding decisions if changes to the plan are required.
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