I was a young Lieutenant stationed at a northern tier missile base and got assigned, along with a staff sergeant, to escort a "hot can", a missile guidance set whose computer could not be erased due to malfunction. Because of this, the MGS was classified and had to be escorted by a two man, one officer team. That is two people, not three as you might think, just another example of the strange titles the government gives to things. We had to be armed with .38 caliber pistols and fly in a government contracted cargo plane escorting the item, which weighed about 1700 pounds and was BIG! The day we were scheduled to go was a blizzard, nearly a whiteout of snow and winds gusting to 60 mph at times. I am at home figuring we're not going. But my boss calls me and says "Hustle yourself to the base, you are going". I politely questioned his sanity and indicate that he should look outside. He told me the Logair pilots fly in weather like this all the time since they resupplied the DEW line in Northern Canada and he equally politely suggested I get my "self"(a euphemism)moving. I felt my way to the base in my car, slipping and sliding all over the road all by myself-everyone else had the good sense to stay indoors. We picked up the MGS in a big truck after getting our weapons and loading them, took the MGS out to flight line. We sat by the flight line for about an hour while the airplane circled above, deciding whether or not to attempt landing(we could not see them-we were monitoring the radio). Finally, we got word that they had decided conditions were too bad to land and we would reschedule for the next day. Finally some good sense! The next day, the only thing that changed was that it wasn't snowing. The wind was about the same. I was again called and told we were going. So I went to the base, got my gun and ammo and went and picked up the component with the Staff Sergeant. We haul it out to the flight line and, shortly thereafter, the plane lands. When I see it, I am not impressed. It was a very old decrepit looking turboprop airplane(a Lockheed L-100 I think). It showed its years, being corroded and tarnished in many locations and even a novice flyer like myself could tell it had lots of hours on it. We got the MGS loaded-there were about 2-3 others on the airplane that were identical. I remembered the STERN advice of my boss not to get it lost, which at the time seemed an silly suggestion considering its size, but I began to understand what he was talking about. The pilots saw we were armed and asked us if the guns were loaded, to which I replied in the affirmative. He insisted that we unload them since we would be in the cockpit with them and the flight engineer, which I could easily understand. I had no official guidance on this, so I complied, as did the Staff Sergeant. We got in the plane and they started the engines and began to taxi to the runway. I could tell this was going to be a hairy takeoff since the winds were blowing 90 degrees to the direction of the runway. I noticed the pilot, copilot and engineer did not fasten their seat belts, but the Staff Sergeant and I did. On the takeoff roll, the airplane was swerving all over the runway. The pilot and copilot did not seem concerned. After liftoff, the plane seemed to be bouncing all over the sky, though the crew still showed no concern. These guys had nerves of steel! After climbing to 10,000 feet and putting the plane on autopilot, with the plane still bouncing around, the pilot, copilot and engineer set up a board between their seats and began playing poker-no kidding! By the way, this decrepit old airplane was creaking and groaning continually. About 20 minutes after takeoff, when the airplane was above the edge of a line of mountains, the bottom dropped out. We lost, from the best I could tell, about 1000 feet in just a few seconds. We were dropping so fast that it felt like I was hanging from my seat belt. In other words, it felt like the plane was dropping faster than I was. The pilot was thrown completely out of his seat behind the center console on top of the engineer, who was also thrown out of his seat. The copilot saved us. He was thrown partially out of his seat, but managed to scramble back in it, jam the throttles wide open and pull us out of a screaming dive. After leveling off and the crewmembers attaining their respective seats, they climbed back up to 10,000 feet, put it back on autopilot and started playing cards again-sans seatbelts. These guys had no nerves! About 10 minutes later, it happened again, though not quite as bad. At that point, the pilot said "Well boys, I guess we better quit playing cards and fly the airplane". They fastened their seat belts-finally!