You will see on your game in the build a ship store some special weapons and planes that all require "rare metal" to purchase.
"Rare Metal" is considered the special money tool for the site that makes it so you can acquire special rare weapons and planes that you can not get any other way other than to purchase from the built in App Store.
As you can see this "Rare Metal" is not only very expensive for so few but you also can see it requires 5 dollars just to purchase enough for the better weapons such as missiles and the rocket launcher. The good news is that people have found many ways to get around this and purchase it for free. Some examples of what they will do is jailbreak their devices (which is not illegal) but then they will download a special software onto their jailbroken device call "IAP Cracker" which allows users to go to the in App Store and receive insane amounts of rare metals and money. Another way that players will obtain this money with a jailbroken device is by downloading an app called "IFile" From Cydia which allows you to go into and change any file within your jailbroken device. One of the files they will change is amount of rare metals you have in your possession by changing the number and saving the file. Please note that what these players are doing is illegal. I personally do not recommend doing such things, not only because it's illegal, but because it ruins your game experience by ridding of the earning money and saving and gradually improving your ship over time. This makes the game more addicting and funner to play. I do understand why others will do these hacks due to the fact that it costs lots of money and eventually wish to try something new or are impatient. There has only been one time in battleship craft history when they gave out free rare metals and that was on there one year anniversary.
(Image provided by battleship craft on Facebook) so unless you were playing on the one year anniversary there is no other way to receive free rare metal. But if you have an older version of battleship craft and still have not updated or can find a way to download an older version of battleship craft, when you go to the App Store and update it and open the app you will receive free rare metals and will say for 1 year anniversary Hope this helps!.