finding, intercepting, and engaging targets without automap, radar, or active sonar

[AdamMil]

Hey, long time no post. I'm trying SH4 with the GFO (game fixes only) mod. I wanted to try playing without map contact updates, but it was hard because it even removed the sonar bearing lines. I tried finding some tutorials for playing without map contact updates, but I couldn't find any good ones. They all seem to be overly simplified. Either the target is plainly visible from the start or else radar or active sonar is used to get an absolute position or they ask the omniscient WO. But what about the case when you're too far away to see or ping it, and you don't have radar?

I played with it for the past 8 hours or so and found a couple of workable approaches. My first approach was to use the information from passive sonar to do a TMA (target motion analysis). I wrote a program to automate the TMA and spit out an intercept vector that would put me in a firing position 1000 yards off the target's side, and on the whole it works fairly well. The main benefit of this approach is that it gives you the target's absolute position, course, speed, AoB, etc. just from passive sonar readings, but it's a bit of a pain to write down the bearings on paper and alt-tab out of the game for a couple minutes to input the data. I also had trouble with my incompetent crew failing to report and track sound contacts despite them being clearly audible, and when that happened the approach degraded because it's hard to be a good sonarman and get accurate readings in addition to plotting on the map and everything else I have to do. Precision is important with this approach.

So my second approach was based on just using the rate of bearing change to find a lead pursuit course with the target. If you're on a lead pursuit vector (i.e. a straight-line course and speed on which you will intercept the target), then the target should remain at a constant bearing. (This is in contrast to a lag pursuit course where you simply keep your bow pointed at the target. Subs are too slow for that to be viable most of the time.) So what I did was:

1. Set my speed to the maximum that I feel is safe/stealthy and turn towards the target bearing.
2. Wait a little while and see how rapidly the bearing is changing.
3. If it's changing, turn in the direction it's changing in such a way as to "overshoot" and hopefully end up on a lead pursuit course, and repeat from step 2. Don't overshoot by more than 30 degrees or so.
4. Otherwise, if it's not changing, I'm on a lead pursuit course.
5. Sail until the target is in visual range (or range of other sensors). If you want, you can slow down as you get closer, for stealth. Just remember to find the intercept course for the new speed.

It's basically a rough version of Newton's method. Example:

• I'm traveling in some direction and hear a target far away on (relative) bearing 120.
• I order ahead standard and turn 120 degrees to starboard. (The target is now at bearing zero.)
• I wait for a little while. As I wait, the target bearing drifts from 0 to 354 (i.e. 0 to -6).
• I "overshoot" by turning 20 degrees to port (to bearing 340). (The target is now at bearing 14.)
• I wait some more. As I wait, the target bearing drifts from 14 to 11.
• It's still drifting towards port so I "overshoot" by turning ten more degrees to port. (The target is now at bearing 21.)
• I wait. The target bearing drifts from 21 to 22.
• Now it's drifting to starboard, so I turn 3 degrees to starboard. (The target is now at bearing 19.)
• I wait. The target stays on bearing 19. That means I'm on a lead pursuit intercept course.

After doing this, the target bearing may still drift very slowly, like one degree every five minutes, because you can't set an exact course in the game. In that case just adjust course again by two degrees maybe. But if the bearing keeps drifting substantially or if the range keeps increasing even though you're on an intercept course, then you're too slow to intercept the target. (You can either speed up or give up.)

The upside of this approach is that it's simpler than using TMA and doesn't require alt-tabbing out of the game. And you don't have to be very precise to get good results. The downside is that it doesn't give you the target's position, course, speed, or AoB, so you still have to figure that stuff out using other sensors and you can't directly sail to a firing position. But it's good to know how to do that anyway. Being on a lead pursuit course takes most of the guesswork out of interception, and when the target gets within 4-8 km or so you can begin roughly estimating its position and plotting its track using the following technique:

• Identify the target as soon as you can, but before then just pick a ship of its class (cargo, warship) with an average mast height.
• Every few minutes, take a stadimeter reading and note the target's bearing. It doesn't need to be perfect, but do the best you can. (In SH3 in rough seas it helps to pause the game when you're centered on the water line.) Radar or active sonar can also give you a position estimate, but may reveal your presence.
• Take the range and bearing and plot a line of that length along the target's bearing on the map, put a mark at the end of the line, and delete the line. (If you're moving or turning it's best to do this while paused, or else quickly mark the position/course of your boat.)
• When you have a few marks, draw a "best fit" line through the marks to estimate the target's track. Position yourself 90 degrees from the track at a good firing distance (say 500m).
• Repeat these steps and keep adjusting the track and your position relative to it. As the target gets closer and you take more readings, the estimated track will get progressively more accurate.
• If you want, you can start the stopwatch when the target is 2-3km away and measure the distance between marks to estimate speed. But if you're really close to the target track you can usually just guesstimate the torpedo lead angle. :-) 4-5 degrees works well for most cargo ships at 600m.

If the target detects you, is unarmed/unescorted, and starts zigzagging you can just surface and sail towards it at speed. If you get within 700 meters, it's relatively easy to score a hit - shoot just as the target starts to turn one way or the other and lead a little bit. Use the magnetic trigger if possible to avoid glancing impacts.

I use this overall approach with success in SH3 + GWX. (I went back to it because SH4 crashed and corrupted my saved games on 2 out of 3 patrols. :-|)