Signalling and identification was crucial to the Japanese art of warfare in the Sengoku (Warring States) period (the period of almost perpetual war from 1450 to 1615).
As armies increased in size, especially during the Warring States period, opponents often had trouble identifying each other and commanders could not recognize important samurai amid the crush of bodies.
Signals became an effective means of controlling troops from a distance during battles, since only coordinated efforts could be successful. Strategies included the use of items such as flags, drums, and conch shells, as well as deployment of fire signals and messengers.
For instance, many samurai and ashigaru affixed a sashimono, or personal banner, on the back of their armor. The family crest (mon) of the army commander was usually painted on the field of the sashimono, which later developed into the more visible vertical banner called a nobori carried by standard bearers into battle.
Similarly, recognizing the potential of messengers, daimyos invested in preparing elite corps of messengers. A commander relied upon his messaging system to convey orders to other generals and ensure timely compliance with directives. These messengers were specially identified by cloaks or distinctive sashimono. For example, Toyotomi Hideyoshi had 29 messengers, all of whom were fitted with a golden sashimono. Nobunaga provided his messengers with a horo, a fabric bag similar to a cloak attached to the back of the armor, in either red or black.
Messenger with horo
During the Warring States period, as the military became more professionalized and battles were plentiful, specialized signaling and other means of identifying entire companies as well as specific figures were instituted. To ensure quick identification of opposing forces at a distance or ready identification of a military leader in poor weather, high-ranking figures had elaborate helmets and other distinguishing characteristics that made them readily recognizable.
Nobori, uma-jirushi and sashimono
At the dawning of this era of many feuding daimyo, the tradition of affixing a sashimono was abandoned, perhaps because such devices could hinder the progress of an elite warrior. Regardless, high-ranking samurai had attendants (standard-bearers) who were charged with carrying the large vertical flag known as a nobori identifying the entire company or unit.
Personalized armor or helmet elements functioned like a crest which might be etched into or painted on European armor to indicate one’s allegiance to a particular ruler. However, overall, Japanese use of banners and flags contrasted with European styles. Apparently, free-flying banners, as commonly seen in recreations of European battles, were not favored in Japan. The most typical banner style of the 15th century and after, the nobori, was a long, vertical piece of fabric that hung from the arm of a pole, which could be easily seen from both sides. Essentially these were larger versions of sashimono made more visible as well as less personal, a change that underscores the increasing grandeur of well orchestrated combat at the end of the Warring States period.
Other types of flags and banners served diverse purposes. Signal flags (as well as fires) could be employed in directing unit movements. Another banner used for identification was the uma-jirushi, or horse insignia, which was worn by the standard-bearer of a daimyo and used to determine whether a leading figure had lost his mount.
In peacetime, banners and flags served to distinguish rank and status of samurai in service to the Tokugawa shogunate. Under the reorganization of the feudal system, samurai rank was equated with banner size. For example, samurai with an income of 1,300 koku were entitled to bear a small flag, while those possessing more than 6,000 koku of annual income could display a large flag. Thus, an entourage approaching the Tokugawa castle in Edo could be identified from a distance. Such banners required three soldiers to serve as bearers, more than the single figure that had accompanied the sashimono of high-ranking retainers in the medieval period. However, due to the dearth of battles, such flags were displayed primarily during processions of daimyo to and from the capital, and represented no hindrance to the typically slow and ceremonious progress of such entourages.