- Battalion 25 - Battalion Chief unit, in command of Battalion 25 and all firehouses in it (including Firehouse 51).
- Ambulance 61 - Ambulance unit, responsible for emergency medical services.
- Engine 51 - Primary firefighting unit, used for water, gear, and personnel transport.
- Truck 81 - Secondary firefighting and rescue unit, used for gear and personnel transport.
- Squad 3 - Technical rescue unit, firefighter members are specially trained for more difficult situations and wider array of emergencies.
Other units mentioned in seriesEdit
- Engine 105 - Assigned to Firehouse 105.
- Truck 63
- Truck 64
- Truck 65
- Truck 66 - Assigned to Firehouse 105. Rival company to Truck 81.
- Truck 67 - Assigned to Firehouse 67. Otis once requested to transfer here.
- Truck 70
- Truck 94
- Squad 1
- Squad 4 - Former assignment to Wallace Boden, Benny Severide, and Henry Mills.
- Ambulance 72
- Ambulance 74
- Ambulance 77 - Assignment to Allan Chout (Temporary relief paramedic to Ambulance 61).
- Ambulance 96
- Battalion 26 - Battalion Chief Dan Wice, secondary chief on scene of structure fire in 3x23.