The description of this video does not give us a specific date, but we're assuming it was taken a decade if not more ago. Judging by the smokiness of the engines, they have to have been a version of B-52Gs or earlier as the Pratt & Whitney J7f water injected engines were well known to smoke like that. Although this doesn't give us an estimated year of the exercise, it does let us know that they were the earlier versions of the Stratofortresses.
As for the video itself, it shows a couple of B-52s along with a KC-135 Stratotanker taking off in what's called MITO (minimal interval takeoff) exercise. Although it was conceived during World War II, this strategy fully flourished during the Cold War.
In case of a nuclear attack and/or full scale bombardment of U.S. bases, this exercise ensures that bombers and tankers are be able to scramble within 15 minutes. Starting with an elephant walk, the fleet would then take off within twelve and fifteen second intervals.
As you'll see here, this exercise (using the older model B-52s) is quite smokey. As for the scary part, it's pretty simple. For one, if you're not the lead plane, you take off after twelve or fifteen seconds of the plane in front of you. As you can imagine, the visibility is quite limited. Plowing through all that smoke is quite nerve-racking.
Also, there's the slipstream. Taking off in such short time after each other causes great turbulence. This could rock the subsequent planes to such an extent that they could lose control and fall out of the sky. This has happened in 1961, 1964 and 1982. Although necessary for readiness, these exercises are quite hazardous.