NYPD CW3 info

So I was listening to NYPD CW3 and I heard a unit come over as "Bus Unit RMP #3346" so I wanted to know if anyone on here could tell me: A.) What is the bus unit? B.) What is their purpose? C.) An estimate of how many cops could be in that unit? D.) What bureau are they assigned to?

and finally E.) What other units use CW3 regularly?