I've heard of Desktop Tower Defense but hadn't tried it until this week. Warning: quite addictive! (there's also now Whiteboard Tower Defense which I haven't tried)
For some Cold War nostalgia (which is a little weird since I wasn't alive/aware during the interesting parts), check out the Wikipedia entry on CONELRAD, precursor of the Emergency Broadcast System which preceded the Emergency Alert System (doesn't the logo for the Emergency Alert System look kind of frightening, like the country's falling apart?) CONELRAD's purpose was to control electromagnetic radiation by shutting down all radio stations except for a few frequencies (a station would stay on the air at one of two designated frequencies for a few minutes, then cycle off and another station would start broadcasting on that frequency) to confuse enemy planes that might try to use the signals to home in on cities. Apparently Japanese planes used a Honolulu radio station to home in on Pearl Harbor.
The British version was the Four minute warning (the estimated time between the detection of a nuclear attack and when it would hit). The announcement is pretty chilling:
This is the Wartime Broadcasting Service. This country has been attacked with nuclear weapons. Communications have been severely disrupted, and the number of casualties and the extent of the damage are not yet known. We shall bring you further information as soon as possible. Meanwhile, stay tuned to this wavelength, stay calm and stay in your own homes.
Remember there is nothing to be gained by trying to get away. By leaving your homes you could be exposing yourselves to greater danger.
If you leave, you may find yourself without food, without water, without accommodation and without protection. Radioactive fall-out, which follows a nuclear explosion, is many times more dangerous if you are directly exposed to it in the open. Roofs and walls offer substantial protection. The safest place is indoors.
Make sure gas and other fuel supplies are turned off and that all fires are extinguished. If mains water is available, this can be used for fire-fighting. You should also refill all your containers for drinking water after the fires have been put out, because the mains water supply may not be available for very long.
Water must not be used for flushing lavatories: until you are told that lavatories may be used again, other toilet arrangements must be made. Use your water only for essential drinking and cooking purposes. Water means life. Don't waste it
Make your food stocks last: ration your supply, because it may have to last for 14 days or more. If you have fresh food in the house, use this first to avoid wasting it: food in tins will keep.
If you live in an area where a fall-out warning has been given, stay in your fall-out room until you are told it is safe to come out. When the immediate danger has passed the sirens will sound a steady note. The "all clear" message will also be given on this wavelength. If you leave the fall-out room to go to the lavatory or replenish food or water supplies, do not remain outside the room for a minute longer than is necessary.
Do not, in any circumstances, go outside the house. Radioactive fall-out can kill. You cannot see it or feel it, but it is there. If you go outside, you will bring danger to your family and you may die. Stay in your fall-out room until you are told it is safe to come out or you hear the "all clear" on the sirens.
Here are the main points again:
Stay in your own homes, and if you live in an area where a fall-out warning has been given stay in your fall-out room, until you are told it is safe to come out. The message that the immediate danger has passed will be given by the sirens and repeated on this wavelength. Make sure that the gas and all fuel supplies are turned off and that all fires are extinguished.
Water must be rationed, and used only for essential drinking and cooking purposes. It must not be used for flushing lavatories. Ration your food supply: it may have to last for 14 days or more.
We shall repeat this broadcast in two hours' time. Stay tuned to this wavelength, but switch your radios off now to save your batteries until we come on the air again. That is the end of this broadcast.
(here's an article about that nuclear script)