I've always wondered how research works. Is it a cumulative point system or is it more sinister than that? In other words, I always want the heavy plasma ASAP - but I can never seem to research it for a couple months. Is there some algorithm stopping me from getting that gun early in the game? Is there a hidden research tree that makes it so if I research other plasma weapons first, my heavy plasma research will be enabled?

According to our R&D boys ( http://www.ufopaedia.org/index.php?title=Research ), it is a cumulative points system, with a different total to reach for each technology, and that total varies from game to game by +- 50% from the average for the technology. Simple and elegant.

There is no prerequisite for the Heavy Plasma, so there is nothing stopping you from starting with the best gun first and working your way backwards. The only problem is that the aliens don't start carrying that weapon right from the beginning of the game. Sure, you may get the occasional alien which has it, but they prefer the Plasma Pistols and Plasma Rifles. Later on they phase out the Plasma Pistols in favor of the Heavy Plasma which becomes the weapon of choice for the rest of the game. We don't quite know what triggers the switchover yet, it could be time, research topics or some other variable.

BTW: I had a X-COM base defense mission today where the only plasma weapon researched was the Heavy Plasma. The equip squad screen let me equip my troops with the Plasma Pistol/Rifle and didn't say anything like "alien artifact" so I thought "what the hay, let's do it". When I got into the mission, the soldiers with the Plasma Pistol/Plasma Rifle couldn't use them because they hadn't been researched yet. What gives? Why does the game even allow unresearched items from showing up? I suppose it picks the first 80 items in the list regardless if the item has been researched. Still, it shouldn't happen.

- Zombie

Yeah, I had a base mission yesterday that I had to do over and over thanks to 1) half of my squad being stuck in some general stores not connected to anything and 2) cryssalids. Every time I had to change out the heavy plasmas that they were automatically equipped with. Maybe someday I'll stop cheesing the game and not reload so often, but I'm not there yet. I hate the fact that every reaction shot from an alien automatically means death for me on hard.

If you have a save in the Geoscape just before the base attack, you could reload to that point and sell off the heavy plasmas before the battleship arrives. (If you haven't researched them yet, start the research with 0 scientists allocated before selling them all off)

Heavy Plasmas are so abundant that there's little need to keep very many in storage, even if you intend to base the core of your arsenal around the heavy plasma later on. Also it's a good idea to get into the habit of spring cleaning your stocks of alien weapons and exotic building materials regularly to keep your bank balance healthy and avoid getting stuffed by the dreaded item limit, which is at its worst during base attacks since you have little say in what you get once the battle starts.

- NKF