In that case you have to learn how to create your own offline challenges.
Warning: Back up everything before you start, especially if you are unsure what you are doing
Step 1, Locate the folder “data” inside your GSB directory
Step 2, Locate 3 folders, “scenarios”, “ships”, and “deployments” inside “data”
add the map
Step 1, Find the custom map, locate that map in “userdir\GratuitousSpaceBattles\custom_scenarios”. Where userdir is depends on which version you have, so the best way is to find it with search.
Step 2, move it to the “scenarios” you located earlier
Step 3, Open up the map and change deployment to the entire map. To do this, find the line player_deployment = a, b, c, d. Replace a and b with 0, c and d with the maximum size.
Step 4, Now go to your missions, you should be able to see your new scenario.
add the ships
You do not need to add ships as long as they are build and saved on your computer.
setting up the deployments.
This step assumes the students has build their fleet on your computer, and that they also saved the deployment.
Step 1, Load the game, Load up the mission and load up a student’s fleet.
Step 2, Move the fleet manually to the opposite end of the screen (mirror), save this file as aifleet_easy.txt, do this for up to 2 more fleets, name them aifleet_medium.txt and ai_fleet_hard.txt
Step 3, find the folder that has the same name as your custom map in “userdir\GratuitousSpaceBattles\deployments”
Step 4, Copy the folder with the same name as your custom map over to the folder “deployment” located earlier
Step 5, Open the deployment files with a text editor (notepad ++), use the replace function to change “angle = 90” to “angle = 270”, this will flip the facing of all the ships creating a true mirror fleet on the other end.
Step 6, Run the game, you should now see the fleet you just made inside the map. You can now deploy normally against any of the 3 fleets.
Step 7, if you need to make more than 3 fleets, you will need to repeat this process.