The 04 level of the Nitro Class ammunition ship is referred to as the Signal Bridge. This is the area where the Signalmen hoist signal flags and pennants on halyards, used signal lamps to flash messages from ship to ship or to send semaphore, via semaphore flags. There are also pelorus which is used during navigation to take bearings on shore or bouy lights, structures, etc. Radar masts and various antenna are also located on the signal bridge.