Bamboo has seen a lot of military use over the millenia. It has been used for:

1. Spear hafts. A complete bamboo pole can be used, or a laminated spear haft can be built from split bamboo. Some ancient Chinese spear hafts were laminated with a wooden core surrounded by pieces of split bamboo. A very simple spear can be made by cutting the end of the bamboo pole at an angle to produce a sharp point; such spears were issued as late as WW2 (as weapons of desperation): i.imgur.com/XQjdXvT.jpg

2. Bows. A self bow can be made of bamboo, horn-and-sinew composite bows can be made with a bamboo core, and laminated bows can be made of bamboo (e.g., the Japanese yumi).

3. Arrow shafts. Since bamboo is strong and fairly straight, it can be used for arrow shafts. A large bamboo can be split to make shafts, or a whole skinny bamboo can be used. Skinny bamboo suitable for making arrow shafts was sometimes grown as a military resource in China (e.g., in a city, so that it could be used in case of siege).

4. Arrow heads. Since bamboo is quite hard (compared to many woods), and can be cut to a sharp edge, it is sometimes used for arrow heads. Bamboo-headed arrows were being used in warfare in the New Guinea Highlands into the second half of the 20th century.

5. Gunpowder weapons. Bamboo has been used for gun barrels, fire-lance barrels, bomb cases, and rocket cases. Bamboo gunbs were being used in China as late as the Ming Dynasty; these were typically wrapped with cloth or cord or wire to strengthen them, and were often intended as cheap single-use weapons.

6. Traps and obstacles. Sharpened bamboo stakes have been used as obstacles and booby traps into the late 20th century (if not later). For a modern example of a similar obstacle using wooden (rather than bamboo) stakes: https://commons.wikimedia.org/wiki/File:A186718.jpg

7. Containers. Bamboo has been used for containers, e.g., for food and water. As the famous quote (often attributed to Napoleon and Frederick the Great), "an army marches on its stomach". Logistics is an important military usage!

8. Construction. Bamboo has been used to construct buildings, bridges, watchtowers, and more, for military use.

9. It's also likely that bamboo knives/daggers have been used as military weapons. These are can be made in the same manner as bamboo spears and stakes, with a sharp point cut at an angle into a round bamboo section, or from split bamboo. Such knives/daggers were still used in New Guinea in the 20th century, and are likely to have been carried in wars.