You need a commercial radio operator license to operate the following:

Ship radio stations if:

• the vessel carries more than six passengers for hire; or
• the radio operates on medium or high frequencies; or
• the ship sails to foreign ports; or
• the ship is larger than 300 gross tons and is required to carry a radio station for safety purposes
• Coast stations which operate on medium or high frequencies or operate with more than 1,500 watts of peak envelope power.
• Aircraft radio stations, except those using VHF frequencies on domestic flights.
• International fixed public radio telephone and radiotelegraph stations.
• Coast and ship stations transmitting radiotelegraphy.