The API link bypasses login and opens your account directly. Be very careful not to let others see your link . Anyone who gets a hold of your API Link has full access of your game session, and are not limited to scrapping or sinking of your ships! See here
DMM recently updated their site and may have changed the use of this method. For more information, please read here (Bypassing the DMM Error Area by Nanamin) and here (DMM Cookies: August 2015 by Dragonjet) for relevant information, or switch to other methods for now. If you have issues, please refer to Tutorial: Troubleshooting before asking questions.
Before posting your question make sure that you have read this page first, understood and are able to ask smart questions. Please do not post a new thread without being able to provide a detailed and verifiable issue.