First Sonar Kill. Exciting Stuff!

[Soundman]

But upon arriving at Honolulu, I find the "End Patrol" selection greyed out. Why can't I end my patrol?? __________________

Make sure you went home to the proper base. You may have been transfered without knowing. Your home base will have a "tilted" anchor, whereas the others will be straight upright. Look closely at your navmap.

Those planes aren't generally worth the trouble, they are fun, but best to avoid them at all costs.