Well, to begin, we need to recognize that when we talk about medieval Japanese castles and sieges, we are not talking about castles that look like Himeji Castle. These architectural expressions of power date to the period of peace following the consolidation of power by the Tokugawa shoguns post 1600. The castles involved in sieges would probably have looked like Sakasai Castle and Arato Castle Depending on the era, Japanese castles were pure fortresses, designed to be used only in times of emergency and located atop mountain peaks; centers of both defense and administration, from which warlords could administer their domains while maintaining the defensive advantages of a fortified base, or purely centers of administrative power, where the defensive features were primarily symbolic instead of functional.

Sieges in feudal Japan followed a similar pattern to those around the world. An attacking army would invest the fortress, while the defenders would retreat within the walls. From there, both sides would wait until changing circumstances forced one side to act, these being the arrival of a relieving army, the arrival of reinforcements for the besiegers, a shortage of food or water, or treachery. Unlike sieges in western Europe or in mainland Asia, there was a distinct lack of siege equipment. While Japanese warlords did have access to man-powered trebuchets, and later cannon, the form of Japanese castle walls made these weapons less than effective. Most Japanese castles were essentially carved from mountainsides, with the steep slopes forming the “walls” of the castle that were then topped with wood palisades. See Shikizan Castle or the increasingly famous Takeda Castle . Wealthier warlords would have the slopes lined with stones that were carefully fitted together, and the palisades would be replaced by wood board walls or clay-plastered walls. Even castles located on flat land would feature walls made of piled earth, topped with a palisade, and possibly lined with stone. The missiles from trebuchets and other siege equipment would not topple these walls.

Most sieges, from what I have read, did not last very long. Many times the defenders would sally forth and attack the besiegers in an attempt to break the siege. These attacks were often a result of declining food or water supplies. There was one siege where the commander of the besieged castle dumped the castle’s water supplies down the slopes of the castle prior to launching a direct attack on the besiegers and driving them off. The besiegers were not idle either. Direct assaults would be launched on the castle, especially when the attackers enjoyed a numerical advantage or when it was necessary to quickly take the fortress. However, this was not especially easy, as Japanese castles employed extensive defense in depth, with multiple baileys providing platforms for defensive archers and, later on, musketmen. See Odani Castle, which withstood multiple sieges by Oda Nobunaga. Besiegers would launch harassing raids and attempt to cut off the castle’s water supplies—especially when the castle did not have a reliable supply of water within its walls. There was also an instance of the deliberate flooding of Takamatsu castle in 1582 by the besiegers during Hideyoshi’s campaigns, where his engineers dammed a river and forced it to flood a castle. Additionally, the besiegers would also attempt to light the castle on fire, a very effective tactic in an age when all castles were essentially made of wood, including the towers, walls, and gates. This was used by Oda Nobunaga to destroy the fortress of Nagashima in 1574. Finally, many sieges were decided by the result of nearby field battles—such as the relief of Nagashino castle following the defeat of the Takeda army by the Oda and Tokugawa in 1574.

In regards to the chances for the besiegers and the besieged, it all depended on multiple factors: the number of men involved, supplies at hand, the possibility of relief or reinforcement, geography, the castle's design and so on. Many sieges would end with the besieging army retreating upon the approach of a reliving force that would change the balance of forces involved. The fall of a castle often meant death for the defenders. Most of the commanders would commit suicide in various ways, or would organize a final, suicidal attack on the enemy. If you were captured, you would be ordered to commit suicide, or, if you were especially despised by the enemy, you would be executed. However, some sieges would not end in mass casualties—take for example the siege of Odawara in 1590, where Hideyoshi’s army essentially partied in full sight of the Hojo’s castle to show off their overwhelming strength. The castle fell without an assault and only the Hojo’s leaders were ordered to commit suicide. On the other hand, the siege of Hachioji castle in 1590, part of the same campaign, fell in one day due to direct assault and led to the deaths of all of the defenders, both men and women, many of whom committed suicide.

Famous castle sieges include the siege of Odawara, 1590, sieges of Nagashima, the sieges of Ishiyama Hongan-ji (among the longest of all Japanese sieges, lasting multiple years due to the supply of Ikko Ikki fortress by the Mori clan), the sieges of Osaka in 1615, the siege of Hachioji, the sieges of Odani castle, and many more. There are multiple sources on Japanese castles online, including the Samurai Archives, and Jcastle: Guide to Japanese Castles. Print sources in English are also available, the most popular being Steven Turnbull’s books on samurai warriors and book on samurai castles, Strongholds of the Samurai. There also translated books, but many of these are from the 1960s to 1970s, and can be a little dated. You can find info on Japanese castles in general introductions to Japanese architecture, including What is Japanese Architecture and Edo: The City that Became Tokyo.

Unfortunately, I cannot directly answer your questions on weapons and equipment. My concentration is architectural history, and I am particularly fascinated by fortifications.

In general principle, sieges went about the same as they did anywhere else: one army sits inside and one army sits outside until one of them gets desperate enough to do something about the stalemate. Or there is some act of perfidy to open the gates. Or somebody rides to the rescue of the besieged. Or the besiegers find something better to do with their time/manpower.

And much like anywhere else, sieges were generally costly pains in the ass for everyone involved and generally nobody sat down to it if they had anything else that could be worth doing, especially if they weren't totally sure they could wait out the enemy before help arrived. If the political or strategic value of a castle or city was very high, that might increase the likelihood of a siege.

Contrary to contemporary popular belief, a ninja did not fly in on a kite and murder everyone inside. Although that would be pretty awesome.

Wikipedia will keep you reading for quite a long time before you even touch on a more legitimate source. I've picked out a few sieges of particular historical importance (or are just interesting to me), but you can read a bunch here:

http://en.wikipedia.org/wiki/Category:Sieges_involving_Japan

In chronological order:

http://en.wikipedia.org/wiki/Siege_of_Nara http://en.wikipedia.org/wiki/Siege_of_Kamakura_(1333) http://en.wikipedia.org/wiki/Siege_of_Osaka http://en.wikipedia.org/wiki/Shimabara_Rebellion http://en.wikipedia.org/wiki/Siege_of_Port_Arthur

Enjoy!

I actually wrote very extensively about Japanese castles and sieges previously.

Description of the mightiest Japanese castles circa 1550 ~ 1600

The coolest parts of Japanese siege defense were definitely the maze of courtyards and kill zones of overlapping fire. I also wrote about how siege doctrine and castle design had similarities as well as strong differences from the designs of other regions.

Siege tactics and weapons in general

I was answering a broader question on comparing the destructive power of medieval siege weapons to modern day weapons and ended up writing a lot about how catapults and trebuchets worked, comparing it to a hellfire missile at one point and covering other siege tactics.

The I talked about Japanese sieges in general

The interesting thing about Japanese sieges were how cordial some of them were. The parleys they would have before sieges began were fascinating. I think the biggest take away is that if either defender or attacker would clearly come out on top, the 'losing' side would simply give up. Attackers would pack up and leave or defenders would surrender the castle without bloodshed.

I imagine this made for an interesting meta-battle of wits and volume where both sides would largely try to convince the other side how doomed they were.

As for your other questions, sieges were a mainstay for Japanese warfare for a long time. Siege battles were not. This is pretty common throughout the world really.

The thing to remember is that simply laying siege is usually a comfortable move for an attacker to make and often very effective. Actually committing to a siege battle is risky as all hell.

The defender's chances of surviving the siege varied widely depending on a whole slew of factors, particularly whether or not the attacker even wanted to take the castle or not. Laying siege to force an enemy to make a move they don't want to is not at all uncommon.

As others have said, Japanese besiegers did not have many intricate siege weapons as topography, doctrine and resources restricted them. The most they would bring would be some mangonels. The biggest tools for siege battles in Japanese times would be ladders, pavises, and fire.

Soldiers themselves would have invariably armed with mostly the same things they carried into a field battle: spears, bows and guns.

Castles were built with defense in mind. The first castles were not nearly as fancy as the later castles were. The first ones were literally made of mud and dirt, largely being dug out of the ground or carved out of the tops and sides of mountains. Japanese defense doctrine believed that more than materials, a castle's strength lay with its location and the surrounding environment. So today we look back and see amazing designs for castles built on islands, at the very peaks of mountains, at sea side, or resting at the side of great mountains.

It was only later that wood reinforcement for more permanent fortifications came to being. Finally, later castles were as much a sign of their owner's prosperity, influence and acclaim as it was for defense. This is when aesthetics came into play as well.

Consequences for failure to take a Japanese castle was much like failing to take any other castle anywhere else. A failed siege battle usually meant the destruction of an army, or at least the end of it as mission effective. The moment the tables turned, nothing prevented the defenders from sallying out and slaughtering a routing besieging force.

Sieges themselves were a large investment of manpower, time and resources. Soldiers needed to be armed, fed, and paid. Multiply this with any substantially large force and it cost entire fortunes to send an army out. Time is also expensive strategically speaking because having an army out on the warpath means one less army defending at home or elsewhere. If medieval Japan was anything, it was cut throat. Neighbors watched each other closely for strengths and weakness, and more importantly, opportunities. (This sort of intelligence work is where ninjas came in!!)

So losing a siege battle or losing the whole army was dangerous. Of course, if you win, the advantages are obvious.

churakaagii and MarcoOokoe already covered battles so I'll just add that personally, the defense of Toishi castle and Odani castle are my favorite siege battles.

Hope this answers everything! Feel free to ask follow up questions!