Screwed...

It looks like your really boned there, but it happens to a lot more people than you'd think, just usually to El Gigante or maybe Verdugo. I can only offer some casual advice, but I guess it's better than nothing right?

For starters, if you can only survive one hit, it will be really difficult with no room for error, but should go like this:

1-hit strategy: As soon as the battle commences, go around the rock straight ahead and pick up the herb there, it should help but wont always be an herb, this might not help you survive more than one hit though, since Pro U-3 does massive damage. When U-3 reaches the vicinity of the red barrel also behind the rock, shoot it to stun and damage it and run for the further cage door thingies, open it and try to meet U-3 on the opposite side of the closer gate.
If done correctly, you should be on the side with the other barrel and he should be trying to bust down the gate to get to you. Create a little space between the two of you and shoot U-3 while he's occupied with your Red9 or TMP, or if you feel it possible, Rifle. After he breaks down the gate, turn and run past the barrel and wait for U-3 to get in radius of it then blast the barrel, allowing you to escape and close the other gate and shoot U-3 while it breaks that one down. After that, skill in dodging and generally knowing U-3's patterns come into play since there are no more tricks up your sleeve. Should you make it to the second part of the fight without using the Broken Butterfly, use the remaining ammunition in it to shoot the parasite for huge damage, then repeat the process of dodging it's attacks and shooting the parasite when you get the chance, Don't try and rush things, there's no room for error. Should you finally kill U-3, congratulations! Good luck fighting Krauser, just remember the Knife Strategy when you fight him, just as easy as normal mode.

2-hit Strategy: Largely the same as the one hit strategy, though there is room to rush things if you think you can, though rushing is still unadvised. As a matter of fact, pretend you can only take one hit the entire battle, when you do get hit and are still alive, you should feel a lot of pressure go away and you'll do just fine the rest of the battle.

Whelp, your screwed

Email me at [email protected] and tell me what guns you have, how many bullets for each, what level, and how much health, grenades, herbs, and generally any thing else that you have in your attach case. I'll tell you what you can do to save your life and beat the game.

I would reccomend going to the merchant and get the R L or if you start a new game buy the tmp and one bullet to a normal 'zombie' then kick em then knife em. Saves lotts of ammo. Or....... On regenerators use 1 striker hit so there leg blows off, back away, wait for it to jump at you, then run towards it and knife them, if they don't save you ammo use dit-man glitch ( equippe striker, and hold b to aim as soon as the curser is green, go to you're attache case and change guns) then you will move twice as fast

You might have to start the game over and knife more and save ammo more like axin123 said.Sorry you might have to start the game over.You might be screwed.

I was in the same position, I just did the cage thing, and when I was out in the open and I busted the crates open and completing obliterated him.

Have you finished the game ????

that happened to me too. i was so stuck. o even bought a rocket launcher. he still didnt die!! but got threw it. i had mine bombs. lots of them. and grendaes too. it ook me a month to get past that level....good luck.