We have a winner!
I wondered about my question from 2017 after seeing a submarine photo on Facebook post. I thought I’d asked the question before, and I did. Re-reading this thread…
I never thought of it before. I looked up USS Los Angeles, and saw that it had fairwater planes. Then I noticed you wrote ‘improved Los Angeles-class’. I looked at them, and saw the bow planes. You learn something new (or old?) every day.
Right, the original Los Angeles-class subs had fairwater planes that did not rotate vertically, so they could not easily break through polar ice. (I think I recall something about the vertically rotating planes being problematic in the earlier subs that had them.) This was not considered a big problem at the time because there were so many older Sturgeon-class subs that were under-ice capable.
But as time went on and the older subs were decommissioned, they decided when they created the improved Los Angeles-class subs (aka the 688i subs) that they needed to also be under-ice capable. This included both a hardened sail as well as the decision to have retractable bow planes in lieu of fairwater planes.
The decision of whether to go with bow planes or fairwater planes is a series of trade-offs. The advantage of fairwater planes is that they allow fine depth control changes without inducing a pitch change on the whole boat like bow planes do (which then needs to be counteracted by the much larger stern planes).
The problem with fairwater planes is that they get in the way and tend to break if you try to punch through polar ice with them, and even rotating them vertically doesn’t completely alleviate this.