The Mission Editor is alot of fun. I create a mod folder and copy and place the data/campaign files in it. There are tutorials about creating custom missions. But you can edit the campaign files without having to create a new mission. The changes would be visible in a normal career. There are three files types: LND - Land: Bases, airbases, coastal guns; RND - Random Layer: Randomly spawned ship traffic; SCR-Scripted layer: Similar to the random layer. Scripting warships should probably be in this layer.
If you open the stock scripted layer you can select and drag units from the explorer window to the map. You can change the properties of units and groups and can run the simulator from the Mission Editor to time the units so they appear where and when you want them to.
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