You will need to edit two files - Go to your steam folder for the game here:

C:\Program Files (x86)\Steam\steamapps\common\Shadow Ops Red Mercury\System

*Note you may need to run the game once in order to create the files etc. So run it and exit the game once.

Then you need to open the two files - Default.ini and RM.ini

In both files - there will be a line in BOTH files listed as the following:

UseVSync=False

You want Vsync on - so change that line in BOTH files to the following:

UseVSync=True

Once changed make sure to save BOTH files.

Done. Once you run the game again you will get 60 fps rather than 400+ fps.

Enjoy the game!