I´ve installed GW 1.1a and UBoat War Ace Campaign 1.8
And have had only one CTD...this have been only one time as I´ve klicked on the surface drive mode on the Crew Management Screen...but how already said only one time

...but I´ve to say I also had this in the stock version of the game more than one time.
I installed it in that way to make it GW compatible
In German from Originally posted by BenQ-the-Hawk out of the German Silent Hunter III Ubi Forum:
Erst Uboat war ace in einen seperaten orden entpacken...
- Loesche den menu ordner
- In den Roster ordner... loesche defside.cfg
- Im Sea Ordner... entferne alle schiffe die schon in Grey Wolves vorhanden sind (einfach vergleichen)
----Jetzt bleiben nur noch die neuen schiffe
----Oeffne die Grey Wolves (schon im spiel) englishnames und germannames dateien(im Sea ordner). Oeffne die neuen (Uboat war Ace) englishnames und germannames dateien.
Kopiere alle namen der neuen schiffe in die originalen Grey Wolves dateien (alle namen die noch nicht da drin stehen).
Die ubout war ace german/englishnames dateien kannst du dann mit den neuen kombinierten datein ueberschreiben.
- Enferne den textures ordner
- entferne Zones.cfg und Scene dat
Translation to english:
First extract UBoat WA Campaign to a seperate folder
- delete menu folder
- in the roster folder ...delete defside.cfg
- in the sea folder...delete all ships already included in GW - then only the new ships from WAC1.8 will remain
- open the GW germannames and englishnames files (in sea folder) + the same files from UBoat WAC 1.8 and copy the names of the new ships from UBoat WAC1.8 into the GW files. Then overwrite the GW files with the ones including additional ships.
- Delete the Texture folder
- Delete the zones.cfg and scene.dat
(tried my best in this translation

)
(I personally copied all Files to one folder then after I´ve made all changes described above, enabled the combined mod with the mod enabler, and game works fine. I´m now on my 18th Patrol and have had only the one CTD, this have been on 2nd Patrol). No probs if Airplanes sighted and so on

...btw just sunk the rodney
Hope this helps, if this has been the problem
Good hunting
WOD