I was thinking to help make the game more realistic. Is having a Maintenance Building to provide standard maintenance and repairs on units as they get higher mileage. This would give us an option to put them in reserves, and buy new units.
This building could be expandable to so many slots, and of course have multiple ones to take as you get more units in your fleet.
This would be a different aspect of the game that would allow us to manage when one of the units break down during a response.