Great game report.
I'd be interesting in seeing the rules, as I am looking to complement my VSF/steampunk skirmish game with a submarine game.
Can I suggest you also then have a look at “Conn Sonar” via their Facebook group? It is focussed on Cold War subs, however, (good though they seem) I think that the sweet spot of the rules might be elsewhere, with more subs on the table than in realistic Cold War Gone hot scenarios. They may work well for close range VSF actions with multiple subs a side, depending on what you are after.