## 3 Applications
### Underwater Exploration  
Underwater exploration is an interesting and challenging use case that helps in managing, conserving, regulating, and using the ocean resources that are particularly significant for a nation's economy and the citizens' well-being [90]. According to the World Bank, the blue economy is the \"sustainable use of ocean resources for economic growth, improved livelihoods, and jobs while preserving the health of ocean ecosystem\" [91]. Underwater exploration mainly deals with the discovery of lost treasures and natural resources. Managing the ocean resources in a sustainable manner is crucial for a nation, as these resources are to be around for the successive generations as well. Based on [92], nearly 14 percent of the U.S. near the coast generates 45 percent of the nation's total GDP. \"NOAA Ocean Exploration\" is the only federal program by the U.S. dedicated to exploring the unknown or poorly known areas of the deep ocean [93]. Matsya 600 is a part of India's \"Deep Ocean Mission\" to discover rare minerals. This is a submersible vehicle under development that can go up to a depth of 6000 m [94]. Similarly, various nations are conducting research on exploring the underwater resources. However, underwater exploration poses several challenges with respect to the nation's security aspects as well. Hence, the data generated and collected should be secure and transparent.  
Blockchain technology can be integrated with the IoUT, thus enabling the exploration of underwater resources in a secure, transparent, and traceable manner. The immutability characteristic of blockchain primarily ensures that the data, once uploaded cannot, be tampered with. This particularly helps in guaranteeing that the explored underwater resources are not being misused. PO8 is a blockchain group in The Bahamas that focuses on integrating blockchain, artificial intelligence, and robotics to explore the treasures and tokenize them with NFTs on the Ethereum blockchain [95]. \"Non-Fungible Investment Vehicles (NFIVs)\" are also created, which provide monetary benefits by generating earnings. The traceability and transparency characteristics of blockchain make it an optimal choice even for tuna traceability. Illegal and unreported fishing can be alleviated to a great extent with the help of blockchain technology. The authors in [96] proposed a cryptographic protocol named \"DeepOcean\", which uses the \"blockchain-agnostic dark pool\" for cryptocurrencies. Here, different parties can agree for trade without the need of knowing about their order sizes in advance. The existing underwater technologies can be combined with blockchain for effective underwater exploration. A detailed review of the different sensing technologies for underwater exploration was carried out by [97]. Essential ocean variables were also detailed in the review. The authors in [98] presented a preliminary design of a robotic system for autonomous underwater vehicles. Such frameworks have the ability to be adjusted according to the different environments and can help in the durability of the devices. Even though underwater exploration contributes to the nations' economy on a large scale, the research on the integration of booming technologies such as blockchain for the IoUT is still at its infancy. Figure 5 depicts the use cases of the blockchain-enabled IoUT. Table 2 summarizes the applications of the IoUT, the motivation for IoUT applications to integrate with blockchain, and their associated challenges.