Officers assigned to ESU are still police officers and perform the duties of police officers. Besides the rescue side of their job, they also perform what other police depts call "SWAT". To be assigned to ESU, an officer has to have a specialty skill such as welding or in the case of my buddy who was in ESU, spent time in the Transit PD and had knowledge of the subways. As is the FDNY Rescue Companies, ESU is not an easy assignment to get. The large rescue vehicle that the ESU units use carries a lot of gear for their SWAT duties that won't be found on an FDNY rescue vehicle.