Carrier pigeons have been retired by most armies. The last European country to do so was Switzerland, in the 1970s (at the same time it got rid of its bicycle units). China, however, has continued to maintain thousands of homing pigeons for military communications duty. A pigeon can carry up to 75 g (2.5 ounces) for several hundred kilometers (at speeds of about 80 kilometers an hour). The Chinese use them to carry coded messages to offshore island bases, and plan to use them in future conflicts where so much electronic jamming is used that carrier pigeons are the only reliable means of communicating.
Carrier pigeons have been used for thousands of years, but declined in usefulness as the telegraph was introduced in the mid-19th century, and radio in the early 20th. Despite that, carrier pigeons saw lots of use in the two World Wars, particularly in hilly areas that interfered with radio signals. Many nations found it cheaper to use carrier pigeons than radios or telephones.
Modern military radios can better cope with terrain and atmospheric problems, as well as jamming. But there are still some electronic jamming methods that can shut down all radios, although most nations are reluctant to use it (since it shuts down everyone's radios.) The Chinese, however, consider the carrier pigeons as a backup device that might come in handy.