We are approaching RP Echo and are currently just outside the first convergence zone. At a simple level, convergence zones are ring shaped areas surrounding a sonar receiver where sound can be detected as it travels in a curved path through water. Convergence zones only occur in deep water, and the distance between them varies according to environmental factors-as a general rule however, they are around 30nm apart.

Looking at our frigate with the 'Underwater Sensors' map setting on, we can see a shaded green circle representing the convergence zone. In some cases you may see multiple convergence zones, but in this case there is only one.

Since the submarine we're now hunting is armed and dangerous, we want to maximise the distance at which we detect it. The convergence zone effectively extends the range of our hull sonar, so to take advantage of this we should slow down so that our passive sonar is able to listen effectively.

We have quite a lot of area to cover, and a limited amount of time. To cover more ground, we can use sprint-drift movement. Open the speed and altitude dialog by pressing F2 and check the box titled 'Sprint and Drift', then move the speed slider to set your desired average speed at 12 knots. Your crew will then alternate between 'drifting' at creep speed to listen for contacts, and 'sprinting' at flank speed to cover ground. The duration of each sprint phase and drift phase will depend on the desired average speed. This is a trade-off that sacrifices continuous sensor coverage for speed over ground.

Configure your ship to sprint and drift directly towards RP Echo; if you wish you may use active sonar to detect the target--but remember this will also give away your presence and location; and unlike the last one, this target is armed.