all good point as noted above.
always check the DB level and layer since they impact how far you can detect.
U.S. subs are generally quieter can detect enemy subs farther, so important to go slow 5 knots/ultra quiet right away and then just search in a zig zag pattern towards last known contact trying various depths above and below any layer.
If you think the target sub is far, you can also use the sprint/drift technique. Sprint forward at 10-15 knots for 1-2 km, then slow to 5 knots/ultra quiet and search the area. Use with care though since going fast makes you easier to detect by enemy subs.
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