You really need to install the game on an SSD. Even an SSD plugged in via USB 3 will be superior to your hard drive. http://www.amazon.com/Transcend-Military-Tested-External-TS1TSJ25M3/dp/B005MNGQ6C/ref=sr_1_8?ie=UTF8&qid=1462760314&sr=8-8&keywords=usb+3+ssd+external
I'm sure there's cheaper ones, but that'll do the job nicely.
My IT department just deployed these to all Macs in my office for use with Time Machine:
By "just" I mean yesterday was the first wave for anyone that was in-office, but so far it seems pretty neat and of course it could be used as a normal external drive rather than Time Machine if that's what you're after.
This is Amazon UK, but I have one of these:
https://www.amazon.co.uk/Transcend-Military-Grade-Shock-Resistance-Portable/dp/B005MNGQ6C
You can get them in larger sizes than 1TB too, and there may be newer versions available. Look around, the Transcend Storejets are decent :)
What about the Transcend one?
This doesn't really have anything to do with the Navy, but for what it's worth, this is the one I have.
Yep. Here you go.