Musing on Yoshimoto’s Very Bad Day

I’m thinking about writing a variant of Tilly’s Very Bad Day for the Japanese “Age of Warring States” (Sengoku Jidai). Samurai, mounted Samurai with bow or lance, Ashigaru, firearms, that kind of thing.

What follows is a set of design notes examining how Tilly’s Very Bad Day (TVBD) maps onto large battles of Sengoku-period Japan.

To be honest I don’t think Tilly’s Very Bad Day needs extensive mechanical change and the rule align closely with Sengoku warfare — provided they are framed and applied with the right assumptions.

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Name

I have a simple naming criterion for Tilly’s Very Bad Day variants: they are named after a capable general whose career — and often life — was cut short by decisive defeat in battle. After all, in the original Tilly’s Very Bad Day, Johann Tserclaes, Count of Tilly, actually died as a consequence of his defeat.

That sets the bar. I need a commander who was:

• competent and respected,
• defeated decisively in a single battle, and
• personally ruined or killed as a direct result.

One candidate stands out far above the rest: Imagawa Yoshimoto — hence Yoshimoto’s Very Bad Day (Imagawa being the family name, Yoshimoto the given name).

Imagawa Yoshimoto (1519–1560) was no reckless fool. He was a capable, respected, and successful daimyō, head of one of the most powerful Sengoku coalitions, and an experienced commander by the standards of his age.

Yet at the Battle of Okehazama he was caught by surprise and killed outright. His campaign plan was sound by contemporary norms, and his army was numerically superior — but a sudden, well-executed attack shattered his force.

The consequences were immediate and dramatic. Imagawa power collapsed almost overnight, and the course of Japanese history was permanently altered.

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Period

My aim is to write a set of rules for large battles in Sengoku-period Japan. In Japanese historiography, Sengoku Jidai denotes an era of chronic civil war, political fragmentation, and intense military experimentation, conventionally dated from c. 1467 to 1615.

I’m specifically interested in the period in which firearms played a significant role.

Firearms first appeared in Japan during the 13th century Mongol invasions, but their impact was limited. The decisive shift came after the arrival of the Portuguese in 1542, which led to widespread adoption of the teppō. By the 1560s, firearms were being employed in large-scale battles. In the year 1567, Takeda Shingen announced that “Hereafter, the guns will be the most important arms. Therefore, decrease the number of spears per unit, and have your most capable men carry guns”

The Battle of Okehazama — where Imagawa Yoshimoto met his end — immediately predates the heavy, systematic use of firearms. That makes it a clean conceptual entry point: it sits just before the transformation of Sengoku warfare.

Accordingly, Yoshimoto’s Very Bad Day covers the period from 1560 to 1615, encompassing the rise of firearm-dominated battlefields through to the final consolidation of Tokugawa power.

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Reframe the core unit concept: from “brigade” to sonae

At heart, this is largely a matter of terminology.

A Japanese sonae is functionally equivalent to a Western brigade: a large tactical formation under a single commander. Renaming the core unit does not, by itself, require mechanical change. However, the reframing is still useful. Sengoku sonae were conceived as combined-arms packets that could screen, probe, skirmish, and then commit. I need to consider this when tweaking TVBD for the east.

Conclusion: Recycle existing troop types and see how far that gets me. Pike+Shot for mixed formation sonae including men with yari, men with firearms, and optionally mounted samurai. Shot for detached troops with firearms. Dragoons for mounted infantry – a common pattern for mounted troops. Horse for charing mounted Samurai with yari. Light Horse for those preferring to skirmish with bow or fire arms. I might rename them to suit the period.

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Firepower for disruption

In Japanese firepower was not expected to destroy the enemy but instead to disrupt them. Firearms unsettle and disorganise. Close combat delivers the decision.

Luckily, disruption is already modelled through resolve loss of TVBD. Firepower hits on relatively poor numbers compared to melee, meaning that shooting rarely routs units outright. Instead, it degrades resolve and cohesion. Melee is decisive — particularly after firepower has softened the target. Units entering melee with reduced resolve are at a clear disadvantage.

Conclusion: TVBD already treats firepower correctly for the Sengoku period.

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Ensure depth and reserves are rewarded

Sengoku-period armies deployed in elaborate formations with fancy names. Examples are: Ganko (‘birds in flight’), Hoshi (‘arrowhead’), Saku (‘keyhole’), Kakuyoku (‘crane’s flight’), Koyaku (‘yoke’), Gyorin (‘fish scales’), and Engetsu (‘half moon’). These textbook formations were theoretical in nature but none-the-less informed actual tactical deployment.

Personally I believe the specifics of these textbook formation are not important. The important bit, something they all share, is that armies were deployed in depth, with mutually supporting sonae, and utilised specialist sonae for certain roles within the army formation.

TVBD already encourages depth of deployment:

• Support rules favour stacked deployments
• Fresh units behind the line are valuable
• Rally-backs create elastic fronts
• Early commitment of all forces is penalised

In TVBD both infantry and cavalry deploy in multiple lines, because units benefit from mutual support rather than frontage alone. Although 17th-century European infantry often deployed in chequerboard patterns, this is emergent behaviour rather than a mandated formation under the rules.

Sengoku armies differ mainly in emphasis, not structure. Players should think in layered deployments — screen, main body, reserve — but the rules already support this.

The specific support rules might have to change. A sonae should be supported by any other sonae, rather than having different rules for cavalry and infantry. But sonae should require supporting troops directly behind and on at least one flank. This encourages the deep, and often complicated, army formations.

TVBD has the specialist units (shot, horse, light horse) that Sengoku-period armies need, although they might be renamed.

Conclusion: TVBD already models depth and reserves effectively; Sengoku play requires reinterpretation, not redesign.

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Allow for commander-in-chief and sub-commanders

For sub-commanders, Sengoku practice aligns neatly with TVBD assumptions. Officers fought with their men, and command distance works as written.

The commander-in-chief is more complex. In Sengoku warfare, large armies were increasingly directed from a relatively static headquarters (“Command from the Enclosure”), with control exercised through pre-battle planning, messengers, and signals. Forward command existed (“Command from the Saddle”), but was the exception rather than the norm and came with some risk.

TVBD already contains a useful abstraction for this in its separate Commander-in-Chief rules, introduced for the Bolivar’s Very Bad Day variant.

Conclusion: this is an area where Sengoku may warrant a default variant — but the mechanism already exists in a variant.

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Cavalry be primarily exploitative, not decisive

Sengoku cavalry struggled against steady infantry frontally, but excelled at:

• exploitation of weakened units
• flank and rear pressure
• pursuit of broken enemies

I believe TVBD cavalry already behave as Sengoku cavalry should. Shock cavalry are devastating against disrupted targets, not intact lines. Light Horse are fragile, but dangerous when used correctly.

Morale erosion from routs creates exactly the kind of cascading vulnerability that cavalry historically exploited.

Conclusion: Cavalry require no mechanical change — TVBD cavalry already function correctly. But mixed formation sonae with integrated cavalry needs some thinking.

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Samurai as scarce force multipliers

About 1/3 of an Sengoku-period “Samurai” army were actually samurai. But they were often split up to strengthen each sonae. Relatively few units would be pure samurai and these would be elites.

This is already baked into TVBD as unit quality. Pure ashigaru units would be inferior. Mixed units of ashigaru and samurai ordinary morale, and pure samurai units superior.

Superior units act as genuine force multipliers, and even a single one can decisively influence a battle. Scarcity is enforced through cost and army list caps.

This models Sengoku samurai far better than rulesets that flood the table with elite troops.

Conclusion: full alignment; no changes needed.

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Emphasise personality friction in sub-commanders

Commanders of all periods have certain foibles. Those of the Sengoku-period we no exception. Reflecting these personal characteristics in the rules could add flavour.

TVBD already includes optional commander attributes, with theatre-specific variants:
Musing on Commander Ability in Tilly’s Very Bad Day
Musing on Commander Special Attributes in Bolivar’s Very Bad Day
Campaign Cards in Populous, Rich, and Rebellious – English Civil War Campaign
Draft Campaign Cards for the Vulture’s Feast

Conclusion: The underlying machinery is already present and Sengoku flavour can be added through labels and presentation.

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Overall conclusion

Actually, having looked at it, I think Tilly’s Very Bad Day already models large Sengoku-period battles extremely well.

What the analysis above revealed is that I have to made some tweaks to get a Sengoku variant, including:

• Rename unit types to suit the Sengoku-period.
• Revise support rules to reflect very deep combined arms tactical formations
• Include C-in-C rules and support both “Command from the Enclosure” and “Command from the Saddle”)
• Have a think about mixed formation sonae with integrated cavalry.
• Add Sengoku-period personality to commanders

Doesn’t seem like a big leap.