Final draft for phase 1
(Don’t really know which part of your Submarine warfare is for phase 1 but anyway this is an attempted summary to your essay :-D)
Submarines fire in opening-fire, selecting a target surface ship and hitting on four or less. Losses on enemy are removed immediately unless enemy Destroyer(s) present.
From second cycle of combat, each Destroyers may “screen” out one surface ship of their power when targeted by a submarine, potential hits goes against that ship instead.
Each Destroyer has two ASW (Anti-Submarine Warfare) rolls. A “search” roll is rolled after selecting a target Submarine and succeed on four or less. Once found, an “attack” roll hit on two or less. Each roll is performed separately. A unit cannot use both of its ASW “attack” roll on the same enemy unit.
Surviving and unfound Submarines can submerge to end combat and remain in the sea zone, or conduct further combat. If it conducts further combat it is automatically found without any “search” rolls.
From turn 4, each US and UK planes are also given 2 ASW rolls each. Bombers may only use their ASW rolls as “search” rolls. From turn 6, each US and UK ASW “attack” rolls hit on three or less.