Final answer:
The tool commonly used with a Halligan in firefighting operations is a fire axe. Together, they form a combination known as the 'irons' and serve complementary functions during forcible entry and other firefighting scenarios.
Step-by-step explanation:
When using a Halligan, the other tool commonly used in conjunction with it is a fire axe. The combination of these two tools is often referred to as the "irons" in firefighting, where the Halligan is used for prying, twisting, and punching, while the fire axe can be used for chopping and also as a striking tool for the Halligan when more force is needed during prying operations.