The United States launched the first nuclear powered submarine. It instantly antiquated decades of antisubmarine warfare that had developed during the Second World War. Admiral Hyman Rickover was to oversee the development of a new nuclear navy, and create a third, and seemingly invulnerable arm, in the American nuclear triad. Ultimately, the Soviets would follow suit.
Time: Mid War
Removed after event: Yes
One of those “for the remainder of the turn” events that is best dealt with by playing it on the last Action Round. An AR7 play of Nuclear Subs will still hurt, since permitting any battleground coup is unpleasant, but the US player may not have planned for it (perhaps he had planned an AR7 play or a Space Race discard), and the US player may not in fact even be able to use it (if he has a scoring card left).
So Nuclear Subs is not a big problem when you draw it. It’s much more dangerous when the US headlines it against you, causing your African battlegrounds to tremble in fear. Against such a headline, there are several possible responses. The best is to overwhelm the US with threats everywhere else. Coups are still restricted geographically by DEFCON, and because they take up your entire Action Round, a round spent defending against influence into Europe or Asia is a round where the Nuclear Subs must stand idly by.
I also like to keep DEFCON high: this can mean either playing SALT Negotiations (double bonus by imposing a -1 on all coups), or just leaving DEFCON at 3 at the beginning of the turn. This allows you to respond to the US battleground coups with a coup of your own: rather than allowing them the last word over and over again, you can choose a country to retaliate in. This can even make Nuclear Subs a detriment for the US, as their coups no longer drop DEFCON and lock you out of a response coup.
Depending on the likely target of the US coups, non-battlegrounds become quite lucrative. If you control the right ones, you can consistently respond to the US coups with realignments. The US will be hesitant to coup non-battlegrounds during the turn, and even if you can’t set up a realignment you can often grab enough countries to deny Domination.
Occasionally you can pull off a fancy play with Yuri and Samantha, Latin American Death Squads, or even Cuban Missile Crisis, though I find such circumstances to be rare.
Finally, there is no better feeling than being able to harmlessly dump CIA Created, ordinarily a DEFCON suicide card, after the US plays Nuclear Subs. (This is incidentally a good reason to play Nuclear Subs yourself, say on AR6, so that you can dispose of CIA on AR7).
Given the risky nature of coups, this event is best for taking over a USSR-controlled Africa, or perhaps getting into South America if you have been locked out entirely. 1-stability countries are near-guaranteed successes on coups, but 2-stability countries are much more risky.
Beware that couping is an action without flexibility. (An alternative way to put it is that coups are “expensive” in terms of Action Rounds, compared to direct influence placement.) You can’t coup a little bit here and place some influence there. By committing yourself to coups, you expose yourself to ripostes elsewhere on the board. Against a good USSR player, you will often find yourself agonizing over whether to respond to the USSR (thereby wasting your Nuclear Subs) or to coup (thereby giving the USSR free rein). A US player too aggressive with her Nuclear Subs will often simply run out of Action Rounds and cards.
On the other hand, Nuclear Subs is still a fine headline even if you don’t intend to coup on every Action Round. As is generally true in Twilight Struggle, sometimes the threat is worse than the execution. The mere possibility of Nuclear Subs coups can compel the USSR into a premature Africa Scoring or other suboptimal plays.