There were full time warriors (koa). A powerful mo`i (leader) could have 2,500 koa under his command and with alliances, ali`i (nobles) and militia to call on an army could number ten thousand warriors.
Hawaiian military organization was based on multiples of four (40 men were a ka`au, 400 were a lau, 4,000 were a mano).
There was sometimes single combat between individual champions. Battles would involve melee weapons but also slings. Women would flank the battlefield and act as medics ready to pull out a wounded warrior and treat him and also provide water. They might also join the battle and there were some women fighters.
Amphibious operations were routine. Outrigger canoes could carry almost 30 warriors.
Men wore loin cloths and the ali`i nui (the top brass) wore mahiole and sometimes cloaks. The mahiole are designed to taunt. The idea is to say my hat looks like it would be so easy to swipe off my head, why don't you come here and try! Ali`i who were captured might be sacrificed to a god. Their bones might be made into weapons and their mana (spiritual energy) would be absorbed by their opponent. Kahuna (specialists in any field but in this context clerics) believed they could also intervene with the gods on behalf of their mo`i through sacrifices or by chanting enemies to death. I don't know if this was ever done on a battlefield or only done remotely.
Troops would be in formations and ka`au were sometimes specialize for things like tracking, pursuit, etc.
The idea was for ali`i to "take possession" of ahupua`a (which were sort of like fiefdoms) and the commoners might stick around and work for you although they were free to pick up and leave if they didn't like the aimoku (local lord in charge of the ahupua`a). The more ahupua`a you control the more tribute you get. But Kamehameha (who was waging wars pre-contact as well as post-contact) deliberately destroyed food sources as he went so there wouldn't be food for enemy armies. This lead to famine.
Other cool trivia: On O`ahu there were beacons atop the Pauoa ridge (Honolulu area) that were meant to warn against invaders, just like Gondor.
There were already versions of the Law of the Splintered Paddle around (thou shalt not harm women/children/elderly sitting by the side of the road when you invade) but we know Kamehameha didn't adhere to this.
I've been studying this because I am making a game that centers around the Battle of Nu`uanu. My favorite source is The Battle of Nu`uanu, 1795 by Neil Bernard Dukas. Feel free to ask more specific questions and I'll crack open my other sources.
