None of them are official 3rd-Edition rules (except Submerging Subs), but they are tried & tested “House Rules” that a great many players use to even the odds & generally spice things up. You can add whatever rules you want to the game when you play with your friends, but these & many others–call them “semi-official”–have been “playtested” extensively and other players can tell you pretty accurately how they’ll affect your game.
In RR, USSR basically skips the Combat Move & Combat portions of their 1st turn, going straight to NonCombat from Purchase Units.
2-Hit BBs (grrrrrr :evil: )are exactly like GeZe said–all BBs have 2 “lives” as it were and must take 2 hits in a single battle to sink. In some versions, the BB hit only once is immediately “repaired” (restored to full strength) after the battle, in others, she stays with only 1 “life” until sunk.
Submerging Subs is more complicated. First of all, it is an official 3rd-Edition rule. In addition to its “Withdraw” ability, each SUB may also “Withdraw in Place”, that is, exit the battle after its counterattack (if any) without moving. The SUB is no longer subject to attack, but “pops up” after the enemy’s Combat round is over and remains in place until its own Combat Movement turn comes around. If it doesn’t move out of the SZ, it must do battle on its Combat round with the enemy forces. If another enemy force enters the SZ to join its allies, it must do so on Combat Move & combat occurs against your SUB–but without the other enemy units being involved since its not their turn!Otherwise, the maneuver is the same as Withdrawing, you just don’t go anywhere.
Ozone27