The scrapper is a special vehicle.

Every fight leads to damages. You can recycle the damaged units !

Open the map an move your mouse over some bases.
Sometimes you will find ones, where the number for "wreck iron" or "wreck gold" are not zero.
You can get this iron and gold, if you send a scrapper to this position. Add enough shippment trucks to your fleet, so that you can transport all the resource.