There are a variety of theories as to how the term “hoagie” came to be, but the most popular and most accepted takes place during WWI.
In 1953 Italians where working in a shipyard in Philadelphia known as Hog Island where emergency shipping was produced for the war. The Italians introduced the sandwich by putting various meats, cheeses, and lettuce between two slices of bread. This became known as the "Hog Island" sandwich; shortened to "Hoggies", then the "hoagie".
The hoagie has grown and evolved since WWI growing into a nationwide fan favorite cloaked under many different names. Although no one is 100% sure where the name hoagie came from, it has earned its recognition based on taste and tradition.