What was the M-209 used for during WWII?

The M-209 was specifically designed as a portable field encryption device used during World War II. Its primary purpose was to securely encode and decode messages for military communication, ensuring that sensitive information remained confidential in the face of potential interception by enemy forces. The device allowed for quick and efficient encryption by operators in the field, enhancing the overall security of military operations. Its use was crucial in maintaining the integrity of communications, which was a vital component of strategic planning and execution during the war. The other options do not accurately describe the function of the M-209, as it was not used for communication without encryption, forecasting weather, or transporting troops.