Pre-mission rehearsal uses simulation to walk through a planned mission before it occurs. Unlike general training, rehearsal is mission-specific: it uses the actual mission plan, the actual vehicle configuration, and a model of the actual site. The goal is to identify problems before they occur in the real environment.

Why This Exists

Surprises during a mission are expensive: vessel standby time is costly, schedule disruption affects the entire project, and some surprises are safety-critical. Rehearsal shifts the point of discovery earlier — problems found in the simulator cost time measured in minutes, not hours or days.

Who This Is For

  • ROV pilots and AUV mission planners preparing for complex missions
  • Dive supervisors reviewing dive plans before execution
  • Operations managers assessing mission feasibility
  • Training departments developing mission-specific preparation curricula

What Rehearsal Is (and Isn’t)

Rehearsal Is

  • A specific walkthrough of the planned mission in simulation
  • An opportunity to identify problems with the plan before committing to it
  • A chance to rehearse emergency procedures specific to the mission
  • A shared mental model builder — all team members see the same mission unfold

Rehearsal Is Not

  • General skills training (that happens in the training programme)
  • A check of vehicle readiness (that happens in pre-deployment testing)
  • A guarantee that the mission will succeed — the real environment always differs from the model

What to Rehearse

Mission Profile

Walk through the complete planned mission sequence:

  • Launch and recovery procedures
  • Transit to site
  • Mission objectives in sequence
  • Any complex manoeuvres (entry to confined spaces, precision positioning)
  • Return to surface/dock

Identify: Are there steps in the plan that are unclear, ambiguous, or poorly defined? Ambiguities in a rehearsal plan become ambiguities in the field plan.

Critical Decision Points

Identify points in the mission where decisions must be made:

  • Go/no-go decision points based on observable conditions
  • Points where timing constraints exist
  • Points where resource consumption (power, gas, time) triggers decision thresholds

Rehearse the decisions, not just the manoeuvres. A mission operator who has practiced the decision at the 20% battery threshold will make a better decision in reality.

Emergency Scenarios

Rehearse the most likely and most serious emergency scenarios:

  • Loss of communication at a specific point in the mission
  • Equipment failure (thruster, sensor) at the worst possible moment
  • Diver emergency requiring immediate ascent
  • Loss of station-keeping with divers in water

Principle: Emergency response is fastest when it has been rehearsed. Operators who have walked through the emergency response have a shared plan and don’t need to improvise.

Site Models for Rehearsal

Sources of Site Data

The quality of rehearsal depends on the quality of the site model:

  • Prior survey data — Previous sonar surveys, bathymetric charts
  • Design drawings — For structures and installations
  • Previous inspection records — Known features, obstructions, growth
  • Environmental data — Current profiles, visibility, sediment type

Managing Site Model Uncertainty

Site models are never complete. Rehearsal must account for this:

  • Identify the assumptions in the site model
  • Rehearse what happens when those assumptions are wrong
  • “What if the structure is further north than the chart shows?”

The goal is not to eliminate uncertainty but to prepare operators to handle it.

Rehearsal for Diving Operations

Pre-dive briefings are a form of rehearsal:

  • Walk through the dive plan step by step
  • Identify each diver’s tasks and the sequence
  • Confirm communication procedures
  • Confirm gas management plan (turning points, ascent triggers)
  • Walk through emergency procedures

Documented requirement: Many regulations require a documented pre-dive briefing. The briefing record serves as evidence that the team was prepared.

Dive Simulation Tools

For complex dives, dedicated dive simulation software can model:

  • Decompression profiles for the planned dive and alternatives
  • Gas consumption under different work rates
  • Ascent profiles for different emergency scenarios

Recording and Debrief

During Rehearsal

Record:

  • The rehearsal run (video capture of the simulation)
  • Deviations from plan
  • Problems identified
  • Questions raised by the team

After Rehearsal

Debrief:

  • What problems were identified?
  • What changes are required to the plan?
  • Were all emergency responses adequate?
  • Does the team have a shared understanding of the mission?

Output: Updated mission plan with issues resolved; list of open questions requiring follow-up before the mission.