Mastering naval combat in Like a Dragon: Pirate of the Caribbean is crucial, and upgrading your Goromaru's cannons is key. This guide details how to enhance your ship's most powerful weapons.
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Chapter 2 introduces Honolulu and Madlantis, major hubs where you'll spend much of your time. Upgrading your ship and crew is essential for progressing the story. During the main quest, you'll meet Julie, a mechanic who runs GearWorks in Honolulu. She upgrades the Goromaru, and you can return to her shop (and even recruit her) to upgrade your cannons.
Various materials are needed for different cannon upgrades, obtained by defeating enemies. The four main component types are:

Speak to Julie, select the cannon you wish to upgrade, and equip them via the crew formation menu. Here are the cannon types and their upgrade requirements:
Shark Cannon

The Shark Cannon inflicts elemental damage with a faster reload than some others, but its damage is lower. Consider prioritizing stronger cannons initially, perhaps acquiring this one later for the benefit of recruiting Julie.
Egesta Cannon

This cannon deals damage over time and is strategically useful, especially since you don't need identical cannons on both sides of the Goromaru. Its two-round bursts compensate for its slow reload.
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Laser Cannon

The Laser Cannon is arguably the best weapon. Save your components for its upgrades. Its devastating damage, despite a long reload, quickly eliminates weaker ships and significantly damages bosses.
Super Laser Cannon

The Super Laser Cannon is the ultimate upgrade, requiring rare components obtainable later in the game. Its superior range and power make it worth saving for, particularly for challenging battles in the Pirate Coliseum and against the Devil Pirates.
This concludes your guide to upgrading cannons in Like a Dragon: Pirate of the Caribbean.
Like a Dragon: Pirate of the Caribbean is available now on PlayStation, Xbox, and PC.