Hi @TrainManMike, sure I'm glad to help. I installed that Post War 175 rocket launcher back in 2013 and never got around to posting a write up in this OGR forum about how I made smoke come out. But since @Arnold D. Cribari wanted photos of launchers with lots of smoke, hopefully he's okay with me explaining how it was built in his thread.
The first thing you need to do is make 4 smoke exhaust paths under your Post War 175 launch pad (because there will be A LOT of smoke coming out under your launcher). I used four 1/2" x 4" pieces of wood under the launch pad.
After you landscaped the openings under the launcher it should look something this. These little exhaust openings are small enough that my visitors never notice.
I hope you saw that 3" round galvanized pipe in the first construction photo coming up from under the train table. That 3" elbow goes back to an old fog machine my kids left behind after they grew up. The fog machine was in my garage anyways, so I might as well be using it for something.
I filled its holding tank with "fox juice" back in 2013 and have never needed to fill it since. The fog machine is mounted up under my train table with 1/2" straps. Then I placed the other end of the 3" galvanized pipe over this 2" opening.
After the old fog machine is plugged in, it takes about 5 minutes to fully warm up. You can see the red glowing light on the wired controller in this photo.
Once the red light goes off, the fog machine is ready for action. While my guests are busy working the vintage rocket launching panel, I have my finger on the fog machines "On" button. They have no idea what going to happen next.
While they are desperately trying to launch the rocket you can see the 4 exhaust shafts under the launch pad directing smoke away.
Since its an original Post War175 controller the spring under the rocket is temperamental and the rocket doesn't always launch as its suppose too (and the smoke get bigger and bigger!)
Sure, I could stop the smoke at anytime but that's when I really mess with my now frantic visitors. I tell them if they don't push that little red "fire" button the rocket will explode on the launch pad. The whole time my finger is on the fog machine button making even more smoke that finally engulfs my visitors and fills the train room.
I have to admit, its my favorite Post War accessory when visitors come over and they always remember the experience. Also, it usually means we have to stop playing trains for about 10 minutes until the smoke clears out.
I hope this helps with your project. Let me know if you have any other questions. Have fun with your rocket launching modification and make sure you are not going to set off any fire sprinklers or smoke alarms in your house!
Thanks