I disagree with the earlier doubters - I really like pattern runners - I take them as soon as I can. The way I see, it they're at least as good as a regular T1. If you use them right, just set the gyro ango (left or right turn in the early ones, or flexibly in the later ones) so that the torpedo will 'work up' the target's course, and then set the range. Better to set the range a little bit farther than you think the target is, so it doesn't start it's pattern early (i.e., before the straight-run-hit happens). Here's why I like em:
1) great for keelshots. If the water's high, and the keelshot misses because the target is bobbing, it has a second, and maybe third chance.
2) Helps to eat up the uncertainty in long range shots. In late war, you find yourself taking shots from 3 or 4 (or more yeesh) km away from the target. Here you _need_ to have a pattern runner to help manage the error in firing solution at that range. That's what they're for.
3) Sometimes the pattern causes them to hit another ship (especially if you set the pattern distance to long). The torpedo can stray into another convoy lane and blammo, you've salvaged a bad shot.
4) seems like an overall a better torpedo (just a hunch, but better for premature det, better range, just better tech).
5) instills fear in your enemy. No longer can the merchantman's skipper feel safe when the torpedo zooms by his bow. The bastard thing comes zipping back and forth to torment him and his companions for another 5-10 minutes!
Major caveat: I've found that the pattern runner tends to 'out-run' it's target, if it's a slow or medium ship. For the short pattern (800m), the torpedo gains on the target such that unless you've missed because the target is going _faster_ than you thought, the pattern won't succeed. Ways to correct this include aiming for the stern, using the wide pattern (1600m), or setting the torpedo on slow speed. On the contrary, for fast ships (like a BB), you want the turns to be tight (800m) and the torpedo fast so the target can't slip out of the kill area.
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