Get VASSAL here: https://pirateswithben.com/vassal/
Get the Defense of St. Helens map I made here: https://www.dropbox.com/s/mk2jmgri9pb079h/Defense%20of%20St.%20Helens.vsav?dl=0
Here is the Defense of St. Helens scenario, created by Gustawicyryl: https://www.deviantart.com/gustawicyryl/art/Map-St-Helens-Island-92117099