Submariner is a project under the auspices of the Substrate ecosystem, designed to enable secure, cross-network message passing in decentralized applications. It facilitates interoperable communication between different blockchain networks built on Substrate and beyond. By enabling cross-chain functionality, Submariner aims to enhance the usability and scalability of decentralized applications (dApps) by allowing them to interact seamlessly across multiple blockchain networks. The project prioritizes security and reliability in its architecture to provide robust solutions for developers aiming to implement cross-blockchain integrations.