For .zip files, I use the .zip support built into Windows. For other types of archives, I use 7-zip. I'm think it's probably a bug in the stock game, but I can't be sure.

are these patrols from the menu selected patrol missions or something happening in your campaign play? it may be a buggy patrol mission

They are from the American Career/Campaign.

My mods list

Game Fixes Only Mod v1.1

New Orders Bar Menu

Webster's No Crew Fatigue

Webster's Improved US Torpedo v2

Magnified Hud Dials for v1.5_Large

Bigger Better Protractors

Extra Allied naval bases for Stock SH4 + UBM v3.0

Webster's Ship Manuvering Fix

3000 Yard Bearing Tool (1920x)

SCAF for SH 1.5

MaxOptics3 for SCAF 1.5

Webster's New sonar view for v1.5

Eye Patch for Stock

shSpeech

SOBERS COMPASS MOD VERSION COLOUR

Webster's Eliminate Floating Plankton

Webster's Upgraded Deck Gun v1

No problems to date

Scaf > highly recommended. various options available.

all I can suggest is try a fresh brand new download version of GFO because something isn't right and its not the mod as built because everyone else is running the mod without having the issues you speak of so maybe the download you got was interrupted somehow or had a data corruption in it.

Just to make sure we are not barking up the wrong tree, do you have version 1.5 of the game?

and

Can you play the stock game without problems?

I think that would have been detected. Zip files have integrity checking...

Yes, I should have 1.5. (I have the U-boat missions expansion.) As I said earlier, my initial belief and my current suspicion is that this is a bug in the stock game, but I haven't played the stock game enough to be confident about that. Losing two campaigns to game problems have put me off for now and I probably won't return to it anytime soon. I only posted here because the original poster's problem sounded very similar to mine and I thought there might be a sure fix posted in this thread. As I mentioned, I'm not expecting you guys to solve my problems, and I'm not blaming GFO, but thank you for trying. :-)

That's only if it was corrupted. If the download stopped at any point it'll behave as if you downloaded the whole thing.

I don't like to argue, but try it. Take any zip file, open it in a hex editor, remove a few hundred bytes from the end (to simulate an incomplete download), and then try extracting (or even opening) it.

That's not the same as if you were downloading it though. What you would do in that case is remove items from the mod instead.(Like you remove some ships from the roster or have a CFG file/s missing.)