User blog comment:BasakaNZ/Thoughts and musings on effective ship levelling/@comment-24847681-20140502014351/@comment-106.160.45.60-20140614052052

Sonar is very cheap to make (10/10/10/10 or 10/10/10/20) and the stronger ones raise accuracy by 2, so pile more of them on if your ships are missing subs too much and have the equip slots to spare. There is some sort of bonus for having both Sonar and Depth Charges equipped at the same time, but in my experience, sonar alone is still easily strong enough for the single sub in the first node.

Alternatively, if you can handle spending twice as much resources, put a backup ship with a depth charge in the fleet and just cycle them out for another CL/DD when they become fatigued. It's a bit more annoying in terms of upkeep, but maybe not more annoying than having to bucket occasionally?