The weapon that played a significant role in the military success of the Han dynasty (206 BCE - 220 CE) was the crossbow. The Han dynasty heavily relied on the use of crossbows in warfare, which contributed to their military strength and expansion.

The crossbow was a powerful ranged weapon that offered several advantages over traditional bows. It was easier to use and required less training and physical strength than a regular bow, making it accessible to a larger number of soldiers. The crossbow also had a longer effective range and could pierce through armor more effectively, giving the Han army an advantage in battles against opponents who relied on traditional archery.

The Han dynasty further improved the crossbow's design by introducing innovations such as the "double bow" crossbow, which increased its power and range. The use of crossbows allowed the Han dynasty to field a formidable army and achieve military successes in conflicts against neighboring states and nomadic tribes.

Aside from the crossbow, the Han dynasty also utilized other weapons, including swords, spears, cavalry, and chariots. However, it was the widespread adoption and effective use of the crossbow that significantly contributed to the military strength and dominance of the Han dynasty.