Awareness of blockchain has soared in recent years with the emergence of cryptocurrencies, but the technology has existed for much longer. The linking of blocks, containing cryptographic functions of transactions and data, means that tampering with their contents becomes increasingly difficult as the chain grows – this concept was exploited for document timestamping applications more than a decade before cryptocurrencies became reality. In many implementations, blocks are confirmed by, and stored at, many nodes in different locations, providing a high degree of data integrity. There are, however, many challenges for applying blockchain technologies in tactical networks, particularly due to the constraints of the platforms, the limited bandwidth available among them, and the impact of network partitioning. In this report, the development and principles of blockchains are presented, along with an overview of their weaknesses and vulnerabilities.