What was the name of the WAN set up by the Department of Defense that contributed significantly to the development of internet protocols?

The correct answer is ARPANET. ARPANET, or the Advanced Research Projects Agency Network, was the first packet-switching network, funded by the U.S. Department of Defense. It played a pivotal role in the early development of networking technologies and protocols that eventually laid the groundwork for the modern internet.

ARPANET utilized packets to transmit data across a network, allowing different types of computers to communicate effectively. This innovative approach to data transmission contributed to the creation of essential internet protocols, such as TCP/IP, which remain fundamental to internet communication today. The transition of ARPANET from a military project to a public network helped facilitate the broader development of networking technologies and protocols that underpin the internet as we know it now.

The other options represent significant networks but did not have the same foundational impact on the internet protocols. NSFNET was a successor to ARPANET that expanded the network for educational and research purposes and contributed to the internet's growth. CompuServe and Fidonet were more focused on specific services and forums rather than the development of the foundational protocols of the internet.