That something can be, or is, of use in some certain field, is not an indication that it was intended for that purpose.
I can learn how to shoot a bow and arrow at the local archery range, but that doesn’t mean that the club has the current or even the past purpose of training yeomen to shoot down French knights.
There is also, I would suggest, some risk in assuming that what we have today in the Niten Ichiryu is what Musashi handed down. But regardless of that, warfare at that time had little to do with swordsmen fighting swordsmen as individuals.
Here is something that I wrote in 2000 which applies:
The Sengoku Jidai and the Tokugawa Shogunate
The Niten Ichi Ryu was founded in what might be called “interesting times”. Japan had been in a state of almost constant warfare for over a hundred years and in 1543, a generation before Miyamoto Musashi was born, the gun was introduced to the country. Musashi lived at the end of a tumultuous time, witnessing and participating in the end of the feudal age and the final consolidation of the country by Toyotomi Hideyoshi and Tokugawa Ieyasu. The first of the three unifiers, Oda Nobunaga had been betrayed killed by Akechi Mitsuhide shortly before Musashi’s birth.
The Japan of this time was not a romantic place of sword-wielding knights roaming the countryside looking for adventure. In the sixteenth century the country contained 25 million inhabitants, almost 10% of which were samurai class. This compares to 16 million people in France, and 4.5 million in England. In England about 0.6% of the population were in the warrior class.
Aside from the samurai, Japan’s armies of the day also contained a large proportion of peasants, mostly as lightly armed infantry. Warfare at this time was surprisingly modern. At the battle of Nagashino, Oda Nobunaga defeated Takeda Katsuyori, son of the famous Takeda Shigen. In this battle Oda had 38,000 men with 10,000 of them being gunners. 3000 gunners placed across a stream and behind breastworks used 1000 round volley firing to break the famous Takeda Cavalry. The same tactics were seen centuries later in Europe.
Twelve years after Nagashino, at Coutras in France, Henry IV of England won the day using 300 men armed with pistols and squads of 25 gunners. This battle resulted in the largest loss of men to that date in the French civil war with somewhat less than 3000 dead. At Nagashino about 16,000 men died.
In the late 16th century there were more guns in single armies in Japan than existed in all of England. In 1584 the battle of Komaki featured no cavalry attacks at all, and certainly no heroic single combat between samurai. The fight resolved into trench warfare with both sides dug in firing volleys of shot and exploding land mines. Hardly the romantic ideal of sword swinging samurai.
In the 1590s Toyotomi Hideyoshi invaded Korea, originally with 160,000 men (1/4 of which were gunners) and eventually with up to 300,000 men. At about this same time, the daimyo of Japan built their great stone castles and seige warfare became common.
In 1598 Hideyoshi died, leaving an infant heir. Five daimyo were appointed regents and eventually the most powerful, Tokugawa Ieyasu, forced a confrontation to decide who would take supreme power. At Sekigahara Tokugawa fought the forces under Ishida Mitsunari in a battle that involved quite a bit of prior seige work at various castles to control the main roads. Fifteen years later Tokugawa consolidated his power by defeating Hideyoshi’s son at Osaka. The country was firmly under his control from this moment on and remained unified ever since despite the occasional regional rebellion.
Curiously, after Sekigahara there was room once again for the individual heroic warrior. With the coming of the Tokugawa peace the need for mass armies, mass tactics, trenches, and castles disappeared allowing time for individual study of the warrior arts. Most of the existing koryu budo of Japan were developed and refined after 1600.
copyright 2000, Kim Taylor From Niten Ichi-ryu, a manual of the sword art available from SDKsupplies.com
So let’s take this to the idea of koryu being training in warfare. Is the Niten Ichiryu a good preparation for war? Musashi claimed so, he repeatedly tells us to see the large in the small, to understand the battlefield from the individual combat.
If you agree that form follows function, and if the koryu were for training soldiers for the battlefield, It would follow that they would not be teaching one-on-one swordfighting as their main practice. Yet at the very beginning that was the main practice of Niten Ichiryu.
Trench warfare was mentioned in the Onin War from 1467 in Kyoto, the gun was introduced in 1543 and became dominant on the battlefield within 50 years. If the koryu were to train soldiers or even generals to fight wars, one would expect them to take some notice of these things. I do not recall any writings from Musashi on how to dig and supply trenches, but he did intend that we extend our individual kata lessons to unit movements during battle. So not strategy and logistics, but certainly tactics, and not so much for the invididual soldier in the trenches, but for the commanding general at the battle. Musashi even mentioned tactics when facing guns and arrows from seigeworks. Being a creature of his time, and having participated in battles, he would be thinking of these things when he thought of fighting.
Despite those few mentions, the Form of the koryu is years-long training of individuals in swordsmanship or other outdated and battlefield UN-ready weaponry. It continues to this day in that form, despite modern weaponry.
The Function, therefore, is NOT warfare today, and as has been argued, not warfare at its (koryu’s) conception. The original function is possibly dueling, but that does not explain its continued practice today since dueling with swords is outlawed, and more importantly, not practiced except in some German University fraternities.
If form follows function, and the form has not changed, one could argue that the function has not changed, and that function today likely reflects the function of the original school.
What is the function today? Or, as my sensei asked me on a flight to a seminar in England many years ago, “I have to do this stuff, it’s a cultural thing, but why do you westerners spend your time doing Japanese martial arts?”
Karl Friday suggests there was a self-improvement and enlightenment “function” to the arts at the beginning, and I tend to agree, since, absent dueling, that’s the only thing that explains the continued, and cross-cultural, existence of the koryu “handed down the generations in a form unchanged”.
Here is my syllogism for today.
Some martial artists may be soldiers
(Not all martial artists are soldiers)
Some soldiers may be martial artists
(Not all soldiers are martial artists)
Some things you learn in the martial arts may be useful to you as a soldier
some things you learn taking violin lessons may also be useful to you as a soldier
it is not necessary to learn anything about martial arts to become a soldier
Martial artists are not identical with soldiers
In other words, you don’t need, nor have you ever needed the kind of skills you learn in a koryu for a battlefield.
Musashi for 1645 is the same as Musashi for 2015 in my opinion, but in neither case is the main function to prepare soldiers for a battlefield. While Generals may find things of use in the Niten Ichiryu and in Musashi’s associated writings, they will also find things of use in train schedules and fuel efficiency numbers for transport trucks.
The main use for the Niten Ichiryu and other koryu is to make better people. Our koan is to find out how learning to kill can help you learn to to be a better person, and incidentally to make a better society.