A lot of fire engines use Imron? or another brand of extremely durable paint. If you want to remove scratching, your best bet is Meguar's M105 Ultra Cut Compound (this is in the Professional line, so it is sold in quarts or gallons only). If you'd rather just bee-bop on down to the local Wal Mart or auto parts store to purchase your wares, you can probably find Meguiar's G17216 Ultimate Compound, which is similar to M105, but it is dialed in for the consumer-level paint guy (available in 16 ounce). You can apply either product by hand, random orbital, or rotary polisher. I suspect that you wish to remove haziness on the fire trucks (rather than completely remove the defects), which either product will do.
If the finish looks good enough for your needs, you can go right to protecting the paint.
If not, use Meguiar's M205 Ultra Finishing Polish.
Then, I would follow up with Meguiar's M20 Polymer Sealant.
It is very easy to apply and remove, looks nice, and durability is good.
I think that once you try M20 you (or the people that maintain these rigs) will use it more often.
Even better... and you aren't gonna believe this one, but it is REALLY SUPER KILLER GOOD STUFF....
Instead of M20 or any other wax/polymer/sealant.... try the incredible Meguiar's G17516 Ultimate Quik Wax.
Once the guys try this stuff they will likely use it all the time!!!
It is REALLY nice stuff, and smells like fruit punch (which is the real reason I use it) .