XCOM 2: Terror from the Deep, the sequel to XCOM: UFO Defence was released by MicroPose in 1995. The game came on either on several 3.5" floppy disks or a single CD and ran in DOS. Recently Firaxis released a remake and a sequel.

The original game was difficult even on the easiest difficulty settings and missions usually ended with the squad losing morale, either running off, firing wildly into the nearest friendly unit, or dropping a live grenade and subsequently exploding.

The game is still available form Steam and GOG and playable through Dosbox.

To even things out, we can edit the game's save files and improve our odds a bit.

The save files are stored in subdirectories labelled GAME_1 through GAME_10. If no game is saved the subdirectory will contain a single mostly empty file, DUM.BIN 4.0K in size.

Once a game has been saved the subdirectory is populated with data files.

Contents of GAME_1 subdirectory

ACTS.DAT       ASTORE.DAT     CRAFT.DAT
FACIL.DAT      LEASE.DAT      MISSIONS.DAT
PURCHASE.DAT   SITE.DAT       UIGLOB.DAT
XCOM.DATA      KNOW.DAT       BASE.DAT    
DIPLOM.DAT     IGLOB.DAT      LIGLOB.DAT
PRODUCT.DAT    RESEARCH.DAT   SOLDIER.DAT
UP.DAT         ZONAL.DAT      ALIEN.DAT  
BPROD.DAT      DUM.BIN	    INTER.DAT  
LOC.DAT        PROJECT.DAT    SAVEINFO.DAT
TRANSFER.DAT   XBASES.DAT

Using dhex to look at the SOLDIER.DAT file we can see that it stores information, unsurprisingly, about our squad.

Looking at the information in game, we can see that our soldier's Time Units value is 54 (36 in hexadecimal), which correlates to byte 1A in the SOLDIERS.DAT file for the first member of the squad.

To verify this we can edit the value and then reload the game and see the new value on the soldier's stats page. Changing the value at 1A from 36 to 37 shows up on the soldier's stats page after reloading the game where the Time Units value is now 55.

BASE.DATcontains the information regarding the underwater bases. From our save we can see the name of the base at the beginning of the file followed by some values that save the layout of the base.

Here is a screen shot of the file in dhex and in game

Building a Living Quarters next to the top Sub Pen and saving the file we can see that the value in DB has changed from ff to 01. We can also see that the Sub Pen, which takes up 4 spaces uses a different value for each space, 10 - 13 with 10 representing the top left corner and 13 the bottom right.

The values roughly correspond to the order in the
Build Facilities menu.

After the 36 bytes for each of the squares in the grid, the values store the remaining building time information. Building a Living Quarters takes 16 days, which shows up in FF as 10, which converted to decimal is 16.

Before editing file

After editing the file the Time to complete value is gone

Editing the file to add a new building will result in a build time of 255. This may be because no memory was assigned to store the build time variable, or it may just be in a non obvious location.

Manually comparing changes in the file is a time consuming processes. A python script to copy the files before and after a save and then compare the differences would help speed things up.