Battleship Craft is by no means an economics simulator. The only purpose of currency is to obtain more resource to build better warships, since ships are automatically repaired after a battle free of charge. However, there is a limited economic structure revolving around two currencies.
Resource is the first and most common currency. It can be utilized to purchase guns, aircraft, hull components and accessories. It is vital to success in Battleship Craft.
The primary method of obtaining Resource is to simply battle other warships. Singleplayer missions will yield greater amounts of Resource versus multiplayer challenges. Awards range from 100 Resource to 10,000 Resource. Losing results in no gain, but no loss of resource. While it will be initially slow to procure due to low awards and less capable warships for low-level players, high level playes will find resource easy to obtain. They can also be purchased in the store.
As the costs of weapons rise alongside skill level, it may be practical to share weapons such as Mk45 guns and AAA batteries, all extremely expensive weapons. Since ships challenge others only one at a time, it is practical to remove the armament of one ship and reapply it to another. The cost savings outweigh the inconvenience.
Rare Metal is a premium currency. It is less common and only be used to obtain a colleciton of specialized weapons and aircraft. While helpful, it is by no means necessary for success.
The only way to obtain Rare Metal is to simply buy them. However, in the 1.6.1 update, five free rare metal was given to all players as an anniversary gift.
Due to its high cost and the specialized nature of the weaponry, it is also practical to share weapons and equipment purchased with Rare Metal. The sharing will certainly help on your wallet.