Having trouble solving the crossword clue "Was busy developing systems underground"? Why not give our database a shot. You can search by using the letters you already have!

To enhance your search results and narrow down your query, you can refine them by specifying the number of letters in the desired word. Additionally, if you already know certain letters within the word, you can provide them in the form of a pattern using the symbol "?" to represent unknown letters. Let's take an example pattern: "d?f???ul?".